HUMAN PHYSIOLOGY AND ANATOMY INTRODUCTION.pptx

HUMAN PHYSIOLOGY AND ANATOMY

1. HUMAN PHYSIOLOGY AND ANATOMY 21BTB104T UNIT V Sensory Organs and Endocrine Glands

2. Human Eye Anteriorly the eyes are protected by the eyelids, which meet at the medial and lateral corners of the eye The space between the eyelids in an open eye is called the palpebral fissure. Projecting from the border of each eyelid are the eyelashes. Modified sebaceous glands associated with the eyelid edges are the tarsal glands. These glands produce an oily secretion that lubricates the eye . Ciliary glands, which are modified sweat glands, lie between the eyelashes, and their ducts open at the eyelash follicles. A delicate membrane, the conjunctiva , lines the eyelids and covers part of the outer surface of the eyeball. The conjunctiva secretes mucus, which helps to lubricate the eyeball and keep it moist.

3. Human Eye The lacrimal apparatus consists of the lacrimal gland and a number of ducts that drain lacrimal secretions into the nasal cavity. The lacrimal glands are located above the lateral end of each eye. They continually release a dilute salt solution (tears) onto the anterior surface of the eyeball through several small ducts. The tears flush across the eyeball into the lacrimal canaliculi medially, then into the lacrimal sac, and finally into the nasolacrimal duct, which empties into the inferior meatus of the nasal cavity. Tears also contain mucus, antibodies, and lysozyme , an enzyme that destroys bacteria. Thus, they cleanse and protect the eye surface as they moisten and lubricate it.

4. Structure of Eye The eye itself, called the eyeball, is a hollow sphere. Its wall is composed of three tunics, or layers, and its interior is filled with fluids called humors that help to maintain its shape. The lens, the main focusing apparatus of the eye, is supported upright within the eye cavity, dividing it into two chambers. Fibrous Layer- The outermost layer, called the fibrous layer, consists of the protective sclera and the transparent cornea . The sclera is seen anteriorly as the “white of the eye.” The central anterior portion of the fibrous layer is crystal clear. Vascular Layer- The middle, or vascular layer, of the eyeball, has three distinguishable regions. Most posterior is the choroid , a blood rich nutritive tunic that contains a dark pigment. The pigment prevents light from scattering inside the eye. Moving anteriorly, the choroid is modified to form two smooth muscle structures, the ciliary body, which is attached to the lens by a suspensory ligament called the ciliary zonule, and the iris. The pigmented iris has a rounded opening, the pupil, through which light passes. Circularly and radially arranged smooth muscle fibers form the iris, which acts like the diaphragm of a camera. Cranial nerve III controls the muscles of the iris.

5. Structure of Eye Sensory Layer The innermost sensory layer of the eye is the delicate two-layered retina, which extends anteriorly only to the ciliary body. The outer pigmented layer of the retina is composed of pigmented cells that, like those of the choroid, absorb light and prevent light from scattering inside the eye. They also act as phagocytes to remove dead or damaged receptor cells and store vitamin A needed for vision. The transparent inner neural layer of the retina contains millions of receptor cells, the rods and cones, which are called photoreceptors because they respond to light . Electrical signals pass from the photoreceptors via a two-neuron chain—bipolar cells and then ganglion cells—before leaving the retina via the optic nerve and being transmitted to, and interpreted by, the optic cortex. The result is vision. The photoreceptor cells are distributed over the entire retina, except where the optic nerve leaves the eyeball; this site is called the optic disc. Since there are no photoreceptors at the optic disc, it results in a blind spot in our vision. The rods and cones are not evenly distributed in the retina. The rods are densest at the periphery, or edge, of the retina and decrease in number as the center of the retina is approached. The rods allow us to see in gray tones in dim light, and they provide our peripheral vision. Lens - Light entering the eye is focused on the retina by the lens, a flexible biconvex crystal-like structure. Recall the lens is held upright in the eye by the ciliary zonule and attached to the ciliary body The lens divides the eye into two segments, or chambers. The anterior segment, anterior to the lens, contains a clear watery fluid called aqueous humor. The posterior segment, posterior to the lens, is filled with a gel-like substance called vitreous humor, or the vitreous body . Vitreous humor helps prevent the eyeball from collapsing inward by reinforcing it internally

6. Structure of Eye The human eye is a complex organ that allows us to see the world around us. It is roughly spherical in shape and is located in the eye socket of the skull. The main structures of the eye include: Cornea: The transparent outer layer of the eye that helps to focus light onto the retina. Iris: The colored part of the eye that controls the amount of light that enters the eye by adjusting the size of the pupil. Pupil: The dark circular opening in the center of the iris that allows light to enter the eye. Lens: A flexible, transparent structure that helps to focus light onto the retina. Retina: The innermost layer of the eye that contains light-sensitive cells called rods and cones, which convert light into electrical signals that are transmitted to the brain via the optic nerve. Optic nerve: The nerve that carries visual information from the retina to the brain. Sclera: The white outer layer of the eye that provides structural support and protection for the delicate internal structures. Choroid: The layer of tissue that lies between the retina and the sclera, and helps to nourish the retina. Aqueous humor: The clear fluid that fills the space between the cornea and the lens. Vitreous humor: The clear, gel-like substance that fills the space between the lens and the retina. Together, these structures work together to allow us to perceive light and see the world around us.

7. Optic nerve The optic nerve is a bundle of more than a million nerve fibers that carry visual information from the retina to the brain. It is located at the back of the eye and is responsible for transmitting the electrical signals generated by the photoreceptor cells in the retina to the brain's visual centers. The optic nerve is composed of ganglion cell axons and glial cells, which provide structural support and insulation for the nerve fibers. As the optic nerve exits the eye, it forms a small disc-shaped structure called the optic disc, which is commonly referred to as the "blind spot" because it contains no photoreceptor cells. The optic nerve fibers from each eye join together at the base of the brain to form the optic chiasm, where some of the nerve fibers cross over to the opposite side of the brain. From the optic chiasm, the nerve fibers continue on to the visual cortex, located at the back of the brain, where they are processed and interpreted as visual information. Damage to the optic nerve can result in vision loss, and conditions such as glaucoma and optic neuritis can cause damage to the optic nerve.

8. Optic chiasm The optic chiasm is the point where the two optic nerves from each eye come together and partially cross over to the opposite side of the brain. It is located at the base of the brain, just beneath the hypothalamus. The crossing of the nerve fibers at the optic chiasm allows the brain to receive visual information from both eyes, which is essential for depth perception and binocular vision. Some of the nerve fibers from the right eye cross over to the left side of the brain, while some of the fibers from the left eye cross over to the right side of the brain. After the nerve fibers cross at the optic chiasm, they continue on to the visual cortex, located at the back of the brain, where they are processed and interpreted as visual information. The nerve fibers that originate from the right side of each retina travel to the left side of the brain, and those originating from the left side of each retina travel to the right side of the brain. Damage to the optic chiasm can result in visual field defects or abnormalities, such as tunnel vision or loss of peripheral vision. Conditions such as tumors or vascular malformations can affect the function of the optic chiasm.

9. Optic tract The optic tract is a pathway that carries visual information from the retina of the eye to the brain. It is made up of axons from the ganglion cells of the retina that converge and exit the eye as the optic nerve. The optic nerves from each eye then merge at the base of the brain to form the optic chiasm. At the optic chiasm, the fibers from the nasal (inner) half of each retina cross over to the opposite side of the brain, while the fibers from the temporal (outer) half of each retina continue on the same side. As a result, the left side of the brain receives visual input from the right visual field of both eyes, and the right side of the brain receives visual input from the left visual field of both eyes. After the optic chiasm, the optic tract continues on to the thalamus, which acts as a relay station for sensory information. From there, visual information is transmitted to the visual cortex in the occipital lobe of the brain, where it is processed and interpreted to give rise to visual perception

10. Vision pathway Axons carrying impulses from the retina are bundled together at the posterior aspect of the eyeball and leave the back of the eye as the optic nerve. At the optic chiasma the fibers from the medial side of each eye cross over to the opposite side of the brain. The fiber tracts that result are the optic tracts. Each optic tract contains fibers from the lateral side of the eye on the same side and the medial side of the opposite eye. The optic tract fibers synapse with neurons in the thalamus, whose axons form the optic radiation, which runs to the occipital lobe of the brain. There they synapse with the cortical cells, and visual interpretation, or seeing, occurs. Each side of the brain receives visual input from both eyes—from the lateral field of the eye on its own side and from the medial field of the other eye. Also notice that each eye “sees” a slightly different view but that their visual fields overlap quite a bit. As a result of these two phenomena, humans have binocular vision. Binocular vision, literally “two-eyed vision,” provides for depth perception, also called “three-dimensional” vision, as our visual cortex fuses the two slightly different images delivered by the two eyes into one “picture.”

11. Vision pathway The vision pathway, also known as the visual system or visual pathway, is the complex network of structures and processes involved in receiving and interpreting visual information from the environment. Here are the major components of the vision pathway: The cornea and lens of the eye focus incoming light onto the retina at the back of the eye. The retina contains specialized photoreceptor cells called rods and cones, which convert light into electrical signals. The electrical signals are transmitted from the photoreceptors to the bipolar cells, which in turn synapse with the ganglion cells. The axons of the ganglion cells converge to form the optic nerve. The optic nerves from each eye converge at the optic chiasm, where some of the fibers cross over to the opposite side of the brain. The optic tracts continue from the optic chiasm to the lateral geniculate nucleus (LGN) of the thalamus, which acts as a relay station for sensory information. From the LGN, information is transmitted to the primary visual cortex in the occipital lobe of the brain, where it is processed and interpreted to give rise to visual perception. Additional processing occurs in other visual processing areas of the brain, including the visual association cortex, which integrates information from different visual areas to form a coherent visual experience. Finally, visual information is used to guide behavior and make decisions about the environment. Overall, the vision pathway is a complex and dynamic system that allows us to perceive and interact with the world around us.

12. Structure and function of ear Anatomically, the ear is divided into three major areas: the external, or outer, ear; the middle ear; and the internal, or inner, ear. The external and middle ear structures are involved with hearing only. The internal ear functions in both equilibrium and hearing. External (Outer) Ear The external ear, or outer ear, is composed of the auricle and the external acoustic meatus. The auricle, or pinna, is what most people call the “ear”—the shell-shaped structure surrounding the auditory canal opening. In many animals, the auricle collects and directs sound waves into the auditory canal, but in humans this function is largely lost. The external acoustic meatus is a short, narrow chamber carved into the temporal bone of the skull. In its skin-lined walls are the ceruminous glands, which secrete waxy yellow cerumen, or earwax, which provides a sticky trap for foreign bodies and repels insects. Sound waves entering the auditory canal eventually hit the tympanic membrane, or eardrum, and cause it to vibrate. The canal ends at the eardrum, which separates the external from the middle ear.

13. Structure and function of ear Middle Ear The middle ear cavity, or tympanic cavity, is a small, air-filled, mucosa-lined cavity within the temporal bone. It is flanked laterally by the eardrum and medially by a bony wall with two openings, the oval window and the inferior, membrane covered round window. The pharyngotympanic tube, or auditory tube, runs obliquely downward to link the middle ear cavity with the throat, and the mucosae lining the two regions are continuous. Normally, the pharyngotympanic tube is flattened and closed, but swallowing or yawning can open it briefly to equalize the pressure in the middle ear cavity with the external, or atmospheric, pressure. This is an important function because the eardrum does not vibrate freely unless the pressure on both of its surfaces is the same. The tympanic cavity is spanned by the three smallest bones in the body, the ossicles , which transmit the vibratory motion of the eardrum to the fluids of the inner ear. These bones, named for their shape, are the hammer, or malleus; the anvil, or incus ; and the stirrup, or stapes . Like dominoes falling, when the eardrum moves, it moves the hammer and transfers the vibration to the anvil. The anvil, in turn, passes the vibration on to the stirrup, which presses on the oval window of the inner ear. The movement at the oval window sets the fluids of the inner ear into motion, eventually exciting the hearing receptors.

14. Structure and function of ear Internal (Inner) Ear The internal ear is a maze of bony chambers called the bony labyrinth, or osseous labyrinth, located deep within the temporal bone behind the eye socket. The three subdivisions of the bony labyrinth are the spiraling, pea-sized cochlea, the vestibule, and the semicircular canals. The vestibule is situated between the semicircular canals and the cochlea. The views of the bony labyrinth typically seen in textbooks, including this one, are somewhat misleading because we are really talking about a cavity. A labyrinth that was filled with plaster of paris and then had the bony walls removed after the plaster hardened. The shape of the plaster then reveals the shape of the cavity that worms through the temporal bone. The bony labyrinth is filled with a plasma like fluid called perilymph. Suspended in the perilymph is a membranous labyrinth, a system of membrane sacs that more or less follows the shape of the bony labyrinth. The membranous labyrinth itself contains a thicker fluid called endolymph.

15. Structure and function of ear The ear is the organ responsible for hearing and balance. It is composed of three major parts: the outer ear, the middle ear, and the inner ear. Outer Ear: The outer ear consists of the visible portion of the ear, called the pinna, and the ear canal, which leads to the eardrum. The pinna helps to collect sound waves and funnel them into the ear canal. The ear canal is lined with tiny hairs and glands that secrete earwax, which helps to trap dirt and prevent infection. Middle Ear: The middle ear is an air-filled cavity that contains three small bones, called ossicles: the malleus, incus, and stapes. The ossicles amplify and transmit sound waves from the eardrum to the inner ear. The middle ear is also connected to the back of the throat by the Eustachian tube, which helps to equalize the pressure between the middle ear and the outside environment. Inner Ear: The inner ear is composed of two major structures: the cochlea and the vestibular system. The cochlea is a snail-shaped structure that contains tiny hair cells that are responsible for converting sound waves into electrical signals that are sent to the brain. The vestibular system is responsible for sensing balance and spatial orientation. It includes the semicircular canals and the otolith organs, which contain tiny hair cells that sense movement and gravity. Overall, the ear is a complex and sophisticated organ that allows us to perceive sound and maintain our sense of balance.

16. Within the cochlear duct, the endolymph-containing membranous labyrinth of the cochlea is the spiral organ of Corti , which contains the hearing receptors, or hair cells . The chambers above and below the cochlear duct contain perilymph. Sound waves that reach the cochlea through vibrations of the eardrum, ossicles, and oval window set the cochlear fluids into motion. As the sound waves are transmitted by the ossicles from the eardrum to the oval window, their force is increased by the lever activity of the ossicles. In this way, nearly the total force exerted on the much larger eardrum reaches the tiny oval window, which in turn sets the fluids of the inner ear into motion, and these pressure waves set up vibrations in the basilar membrane. The receptor cells, positioned on the basilar membrane in the spiral organ of Corti , are stimulated by the vibrating movement of the basilar membrane against the gel-like tectorial membrane that lies over them. The “hairs” of the receptor cells are embedded in the stationary tectorial membrane such that when the basilar membrane vibrates against it, the “hairs” bend . The length of the fibers spanning the basilar membrane “tunes” specific regions to vibrate at specific frequencies. In general, high-pitched sounds disturb the shorter, stiffer fibers of the basilar membrane and stimulate receptor cells close to the oval window, whereas low-pitched sounds affect longer, more floppy fibers and activate specific hair cells further along the cochlea. Once stimulated, the hair cells transmit impulses along the cochlear nerve to the auditory cortex in the temporal lobe, where interpretation of the sound, or hearing, occurs. Because sound usually reaches the two ears at different times, we could say that we hear “in stereo.” Functionally, this helps us to determine where sounds are coming from in our environment. When the same sounds, or tones, keep reaching the ears, the auditory receptors tend to adapt, or stop responding, to those sounds, and we are no longer aware of them.

17. Auditory pathway The auditory pathway is the route that sound waves take from the external ear to the brain, where they are processed and interpreted as sound. Here are the major components of the auditory pathway: External Ear: Sound waves enter the ear canal and cause the eardrum to vibrate. Middle Ear: The vibrations are transmitted from the eardrum to the three small bones in the middle ear (the malleus, incus, and stapes), which amplify the sound and transmit it to the inner ear. Inner Ear: The vibrations are then transmitted to the cochlea, a fluid-filled structure in the inner ear that contains hair cells. The hair cells are responsible for converting the vibrations into electrical signals, which are then transmitted to the brain. Auditory Nerve: The electrical signals are transmitted from the cochlea to the auditory nerve, which carries the signals to the brainstem. Brainstem: The signals are first processed in the brainstem, where they are sorted and integrated with other sensory information. Thalamus: The signals are then transmitted to the thalamus, which acts as a relay station for sensory information. Auditory Cortex: Finally, the signals are transmitted to the auditory cortex in the temporal lobe of the brain, where they are processed and interpreted as sound. Overall, the auditory pathway is a complex and intricate system that allows us to perceive and interpret sound.

18. Endocrine Glands The major endocrine organs of the body include the pituitary, pineal, thyroid, parathyroid, thymus and adrenal glands, pancreas, and gonads (ovaries and testes). The hypothalamus, which is part of the nervous system, is also recognized as a major endocrine organ because it produces several hormones. Some hormone-producing glands (the anterior pituitary, thyroid, parathyroids, and adrenals) have purely endocrine functions, but others (pancreas and gonads) have both endocrine and exocrine functions and are thus mixed glands.

19. Endocrine Glands-Overall functions The endocrine system is a complex network of glands and organs that produce and secrete hormones. These hormones regulate a wide variety of bodily functions, including growth and development, metabolism, reproduction, and mood. Here is an overview of the major endocrine glands and their functions: Pituitary gland: The pituitary gland is often referred to as the "master gland" because it controls the functions of other endocrine glands. It produces a number of hormones that regulate growth, metabolism, and reproductive function. Thyroid gland: The thyroid gland produces hormones that regulate metabolism, energy production, and growth and development. Parathyroid gland: The parathyroid gland produces hormones that regulate calcium and phosphorus levels in the blood and bones. Adrenal glands: The adrenal glands produce hormones that regulate the body's response to stress, including cortisol and adrenaline. Pancreas: The pancreas produces hormones that regulate blood sugar levels, including insulin and glucagon. Ovaries: The ovaries produce hormones that regulate reproductive function in women, including estrogen and progesterone. Testes: The testes produce hormones that regulate reproductive function in men, including testosterone. Overall, the endocrine system plays a critical role in maintaining homeostasis, or balance, in the body. Hormones produced by the endocrine glands regulate a wide range of physiological processes and help to coordinate the body's response to internal and external stimuli.

20. Pituitary Gland The pituitary gland is approximately the size of a pea. It hangs by a stalk from the inferior surface of the hypothalamus of the brain, where it is snugly surrounded by the sellaturcica of the sphenoid bone. It has two functional lobes—the anterior pituitary (glandular tissue) and the posterior pituitary (nervous tissue).

21. Pituitary Gland Anterior Pituitary Hormones The anterior pituitary produces several hormones that affect many body organs . Two of the six anterior pituitary hormones in the figure—growth hormone and prolactin—exert their major effects on nonendocrine targets. The remaining four—follicle-stimulating hormone, luteinizing hormone, thyrotropic hormone, and adrenocorticotropic hormone—are all tropic hormones. Tropic hormones stimulate their target organs, which are also endocrine glands, to secrete their hormones, which in turn exert their effects on other body organs and tissues. All anterior pituitary hormones (1) are proteins (or peptides), (2) act through second-messenger systems, and (3) are regulated by hormonal stimuli and, in most cases, negative feedback. Growth hormone (GH) is a general metabolic hormone. Its major effects are directed to the growth of skeletal muscles and long bones of the body, and thus it plays an important role in determining final body size. GH is a protein-sparing and anabolic hormone that causes the building of amino acids into proteins and stimulates most target cells to grow in size and divide. At the same time, it causes fats to be broken down and used for energy while it spares glucose, helping to maintain blood sugar homeostasis. Prolactin (PRL) is a protein hormone structurally similar to growth hormone. Its only known target in humans is the breast . After childbirth, it stimulates and maintains milk production by the mother’s breasts. The gonadotropic hormones regulate the hormonal activity of the gonads (ovaries and testes). In women, the gonadotropin follicle-stimulating hormone (FSH) stimulates follicle development in the ovaries. As the follicles mature, they produce estrogen, and eggs are readied for ovulation. In men, FSH stimulates sperm development by the testes. Luteinizing hormone (LH) triggers ovulation of an egg from the ovary and causes the ruptured follicle to produce progesterone and some estrogen. In men, LH stimulates testosterone production by the interstitial cells of the testes.

22. Pituitary Gland Posterior Pituitary and Hypothalamic Hormones Oxytocin is releavsed in significant amounts only during childbirth and nursing. It stimulates powerful contractions of the uterine muscle during sexual relations, during labor, and during breastfeeding. It also causes milk ejection in a nursing woman. Both natural and synthetic oxytocic drugs are used to induce labor or to hasten labor that is progressing at a slow pace. The second hormone released by the posterior pituitary is antidiuretic hormone (ADH). Diuresis is urine production. Thus, an antidiuretic is a chemical that inhibits or prevents urine production. ADH causes the kidneys to reabsorb more water from the forming urine; as a result, urine volume decreases, and blood volume increases. Water is a powerful inhibitor of ADH release. In larger amounts, ADH also increases blood pressure by causing constriction of the arterioles (small arteries). For this reason, it is sometimes referred to as vasopressin .

23. Pituitary glands The pituitary gland is a small, pea-sized gland located at the base of the brain, just below the hypothalamus. It is often referred to as the "master gland" because it controls the functions of other endocrine glands in the body. Here are the major functions of the pituitary gland: Secretion of Hormones : The pituitary gland produces and secretes a number of hormones that regulate various bodily functions, including growth, metabolism, reproduction, and stress response. Some of the hormones produced by the pituitary gland include:Growth hormone (GH): Regulates growth and development in children and adults. Prolactin (PRL ): Stimulates milk production in the mammary glands after childbirth. Adrenocorticotropic hormone (ACTH): Stimulates the adrenal glands to produce cortisol in response to stress. Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): Regulate the reproductive system by stimulating the production of estrogen and testosterone. Control of Other Endocrine Glands : The pituitary gland secretes hormones that control the functions of other endocrine glands, including the thyroid gland, adrenal glands, and gonads. Regulation of Water Balance : The pituitary gland produces antidiuretic hormone (ADH), which regulates water balance in the body by controlling the amount of water excreted by the kidneys. Regulation of Body Temperature : The pituitary gland produces thyroid-stimulating hormone (TSH), which regulates the body's metabolism and helps to maintain a constant body temperature. Overall, the pituitary gland plays a critical role in regulating a wide range of bodily functions and maintaining homeostasis in the body. Dysfunction of the pituitary gland can lead to a variety of hormonal imbalances and disorders.

24. Thyroid Gland The thyroid gland is located at the base of the throat, just inferior to the Adam’s apple, where it is easily palpated during a physical examination. It is a fairly large gland consisting of two lobes joined by a central mass, or isthmus . The thyroid gland makes two hormones, one called thyroid hormone, the other called calcitonin . Internally, the thyroid gland is composed of hollow structures called follicles , which store a sticky colloidal material. Thyroid hormone is derived from this colloid. Thyroid hormone, often referred to as the body’s major metabolic hormone, is actually two active iodine-containing hormones, thyroxine or T4, and triiodothyronine , or T3. Thyroxine is the major hormone secreted by the thyroid follicles. Thyroid hormone controls the rate at which glucose is “burned,” or oxidized, and converted to body heat and chemical energy (ATP). Because all body cells depend on a continuous supply of ATP to power their activities, every cell in the body is a target. Thyroid hormone is also important for normal tissue growth and development, especially in the reproductive and nervous systems.

25. Parathyroid glands The parathyroid glands are tiny masses of glandular tissue most often found on the posterior surface of the thyroid gland . Typically, there are two parathyroid glands on each thyroid lobe, that is, a total of four parathyroids; but as many as eight have been reported, and some may be in other regions of the neck or even in the thorax. The parathyroids secrete parathyroid hormone (PTH), which is the most important regulator of calcium ion (Ca2+) homeostasis of the blood. When the blood calcium ion concentration drops below a certain level, the parathyroids release PTH, which stimulates bone destruction cells (osteoclasts) to break down bone matrix and release calcium ions into the blood. Thus, PTH is a hypercalcemic hormone (that is, it acts to increase the blood level of calcium ions), whereas calcitonin is a hypocalcemic hormone. . Although the skeleton is the major PTH target, PTH also stimulates the kidneys and intestine to absorb more calcium ions (from urinary filtrate and foodstuffs, respectively).

26. Parathyroid glands The parathyroid glands are four small glands located on the back of the thyroid gland in the neck. The parathyroid glands produce parathyroid hormone (PTH), which plays a critical role in regulating calcium and phosphorus levels in the blood and bones. Here are the major functions of the parathyroid glands: Regulation of Calcium Levels: The primary function of the parathyroid glands is to regulate calcium levels in the blood. When blood calcium levels are too low, the parathyroid glands secrete PTH, which stimulates the release of calcium from bones and increases calcium absorption from the intestines and kidneys. When blood calcium levels are too high, the parathyroid glands reduce the production of PTH. Regulation of Phosphorus Levels: In addition to regulating calcium levels, PTH also helps to regulate phosphorus levels in the blood. PTH stimulates the kidneys to excrete excess phosphorus, which helps to maintain a balance of calcium and phosphorus in the body. Bone Metabolism: PTH plays a critical role in bone metabolism by stimulating the activity of cells called osteoclasts, which break down bone tissue and release calcium into the bloodstream. Vitamin D Metabolism: PTH also helps to regulate vitamin D metabolism by stimulating the production of an active form of vitamin D, which enhances calcium absorption in the intestines. Overall, the parathyroid glands play a critical role in maintaining a balance of calcium and phosphorus in the body, which is essential for normal bodily functions. Dysfunction of the parathyroid glands can lead to a variety of disorders, including hyperparathyroidism (too much PTH) and hypoparathyroidism (too little PTH).

27. Adrenal glands The two adrenal glands curve over the top of the kidneys like triangular hats. Although each adrenal gland looks like a single organ, it is structurally and functionally two endocrine organs in one. Much like the pituitary gland, it has parts made of glandular (cortex) and neural tissue (medulla). The central medulla region is enclosed by the adrenal cortex, which contains three separate layers of cells

28. Adrenal glands The adrenal cortex produces three major groups of steroid hormones, which are collectively called corticosteroids —mineralocorticoids, glucocorticoids, and sex hormones. The mineralocorticoids, mainly aldosterone , are produced by the outermost adrenal cortex cell layer. As their name suggests, the mineralocorticoids are important in regulating the mineral (or salt) content of the blood, particularly the concentrations of sodium and potassium ions. These hormones target the kidney tubules that selectively reabsorb the minerals or allow them to be flushed out of the body in urine. When the blood level of aldosterone rises, the kidney tubule cells reabsorb increasing amounts of sodium ions and secrete more potassium ions into the urine. When sodium is reabsorbed, water follows. Thus, the mineralocorticoids help regulate both water and electrolyte balance in body fluids. The release of aldosterone is stimulated by humoral factors, such as fewer sodium ions or more potassium ions in the blood . The middle cortical layer mainly produces glucocorticoids, which include cortisone and cortisol. Glucocorticoids promote normal cell metabolism and help the body to resist long-term stressors, primarily by increasing the blood glucose level.

29. Adrenal glands In both men and women, the adrenal cortex produces both male and female sex hormones throughout life in relatively small amounts. The bulk of the sex hormones produced by the innermost cortex layer are androgens but some estrogens (female sex hormones) are also formed. The adrenal medulla, like the posterior pituitary, is a knot of nervous tissue. When the medulla is stimulated by sympathetic nervous system neurons, its cells release two similar hormones, epinephrine , also called adrenaline, and norepinephrine (noradrenaline), into the bloodstream. Collectively, these hormones are called catecholamines . The catecholamines of the adrenal medulla prepare the body to cope with short-term stressful situations and cause the so-called alarm stage of the stress response. Glucocorticoids, by contrast, are produced by the adrenal cortex and are important when coping with prolonged or continuing stressors, such as dealing with the death of a family member or having a major operation. Glucocorticoids operate primarily during the resistance stage of the stress response

30. Adrenal glands The adrenal glands are a pair of small glands located on top of each kidney. The adrenal glands produce hormones that play a critical role in regulating the body's response to stress and maintaining a balance of bodily fluids and electrolytes. Here are the major functions of the adrenal glands: Production of Hormones: The adrenal glands produce a number of hormones, including: Cortisol: Helps the body respond to stress by increasing blood sugar levels and suppressing the immune system. Aldosterone: Regulates the balance of fluids and electrolytes in the body by increasing the reabsorption of sodium and water and increasing the excretion of potassium in the kidneys. Adrenaline and noradrenaline: Trigger the "fight or flight" response by increasing heart rate, blood pressure, and respiration. Response to Stress: The adrenal glands play a critical role in the body's response to stress. When the body is under stress, the adrenal glands release cortisol, adrenaline, and noradrenaline, which help the body respond to the stressor. Regulation of Blood Pressure: Aldosterone, a hormone produced by the adrenal glands, plays a critical role in regulating blood pressure by controlling the balance of fluids and electrolytes in the body. Regulation of Blood Sugar: Cortisol, another hormone produced by the adrenal glands, helps to regulate blood sugar levels by increasing the release of glucose from the liver. Overall, the adrenal glands play a critical role in regulating the body's response to stress, maintaining a balance of fluids and electrolytes, and regulating blood pressure and blood sugar levels. Dysfunction of the adrenal glands can lead to a variety of disorders, including adrenal insufficiency and Cushing's syndrome.

31. Homeostasis of Glucose in the body Homeostasis of glucose in the body is maintained by a complex interplay between hormones, enzymes, and organs. Glucose is the primary source of energy for the body's cells, and it is essential that the body maintains a stable level of glucose in the blood. When the level of glucose in the blood rises after a meal, the pancreas releases insulin, which signals the body's cells to take up glucose from the blood and use it for energy or store it as glycogen. Insulin also signals the liver to take up glucose and convert it to glycogen for storage. When the level of glucose in the blood falls, the pancreas releases glucagon, which signals the liver to break down glycogen and release glucose into the bloodstream. Glucagon also stimulates the liver to produce glucose from non-carbohydrate sources, such as amino acids and fats. Another hormone that plays a role in glucose homeostasis is cortisol, which is produced by the adrenal glands. Cortisol increases blood sugar levels by stimulating the liver to produce glucose and by reducing the uptake of glucose by the body's cells. The kidneys also play a role in glucose homeostasis by reabsorbing glucose that has been filtered from the blood and returning it to the bloodstream. This helps to prevent glucose loss in the urine. Overall, the body's ability to maintain a stable level of glucose in the blood is essential for normal bodily functions. Dysfunction of the mechanisms that regulate glucose homeostasis can lead to a variety of disorders, including diabetes mellitus, hypoglycemia, and hyperglycemia.

32. Homeostasis of calcium in the body Homeostasis of calcium in the body is regulated by a complex interplay of hormones, enzymes, and organs. Calcium is essential for a variety of bodily functions, including muscle contraction, nerve function, blood clotting, and bone health. When blood calcium levels drop, the parathyroid glands secrete parathyroid hormone (PTH), which stimulates the release of calcium from bones and increases the reabsorption of calcium by the kidneys. PTH also stimulates the production of an active form of vitamin D, which enhances calcium absorption in the intestines. When blood calcium levels are high, the thyroid gland releases calcitonin, which reduces the release of calcium from bones and increases calcium excretion by the kidneys. Another hormone that plays a role in calcium homeostasis is vitamin D. Vitamin D is produced in the skin when exposed to sunlight and is also obtained from dietary sources. Vitamin D promotes calcium absorption in the intestines and helps to maintain calcium balance in the body. Calcium is also regulated by various enzymes, such as those involved in bone remodeling, and by organs such as the kidneys, which excrete excess calcium from the body. Overall, the body's ability to maintain a stable level of calcium in the blood is essential for normal bodily functions. Dysfunction of the mechanisms that regulate calcium homeostasis can lead to a variety of disorders, including osteoporosis, hypercalcemia, and hypocalcemia.

33. Summarize about auditory pathway of ear and explain how light which falls on eye reaches the optic nerve The auditory pathway of the ear refers to the series of structures and processes involved in the perception of sound. Sound waves enter the ear and are captured by the outer ear, which funnels them into the ear canal. The sound waves then travel to the eardrum, which vibrates in response to the waves. The vibrations of the eardrum are transmitted to the middle ear, where three small bones (the malleus, incus, and stapes) amplify the sound and transmit it to the inner ear. In the inner ear, the sound waves are transformed into electrical signals that are sent to the brain via the auditory nerve. As for how light which falls on the eye reaches the optic nerve, the process involves several structures and processes as well. Light enters the eye and passes through the cornea, which helps to focus the light onto the lens. The lens then further refracts the light and focuses it onto the retina at the back of the eye. The retina contains light-sensitive cells called photoreceptors, which convert the light into electrical signals that are sent to the brain via the optic nerve. The optic nerve carries the visual information from the eye to the brain, where it is processed and interpreted to create the visual experience. In summary, the auditory pathway of the ear involves the capture, transmission, and processing of sound waves, while the visual pathway of the eye involves the capture, transmission, and processing of light waves. Both pathways rely on specialized structures and processes to transform physical stimuli into electrical signals that are sent to the brain for interpretation.

34. Auditory pathway of ear The auditory pathway of the ear is the process by which sound waves are transformed into neural impulses that can be interpreted by the brain as sound. The pathway can be divided into three main parts: the outer ear, the middle ear, and the inner ear. Outer ear : The outer ear consists of the pinna and the ear canal. The pinna is the visible part of the ear that collects sound waves and directs them into the ear canal. The ear canal is a narrow tube that leads to the eardrum. Middle ear : The middle ear is a small air-filled cavity that contains the three smallest bones in the body, known as the ossicles. These bones are called the malleus, incus, and stapes. When sound waves reach the eardrum, they cause it to vibrate, which in turn causes the ossicles to vibrate. The stapes then transmits these vibrations to the inner ear through a small opening called the oval window. Inner ear : The inner ear consists of the cochlea and the vestibular system. The cochlea is a snail-shaped structure that is filled with fluid and contains thousands of hair cells. When the ossicles transmit vibrations to the oval window, the fluid in the cochlea also vibrates, causing the hair cells to move. These hair cells then convert the vibrations into neural impulses that are sent to the brain via the auditory nerve. The vestibular system is responsible for maintaining balance and spatial orientation. Once the neural impulses reach the brain, they are interpreted as sound. Different parts of the brain are responsible for processing different aspects of sound, such as pitch, volume, and location.

35. Explain how light which falls on eye reaches the optic nerve Light enters the eye through the cornea, the transparent outermost layer of the eye. The cornea helps to focus the light and directs it through the pupil, a small opening in the center of the iris, the colored part of the eye. The iris controls the amount of light that enters the eye by adjusting the size of the pupil. After passing through the pupil, the light passes through the lens, a clear, flexible structure located behind the iris. The lens helps to further focus the light onto the retina, a layer of specialized cells at the back of the eye. The retina contains two types of photoreceptor cells, rods and cones. Rods are sensitive to light and dark and are responsible for vision in dimly lit environments, while cones are responsible for color vision and work best in bright light. When light reaches the retina, it is absorbed by the photoreceptor cells, which convert the light into electrical signals. These signals are then transmitted to the ganglion cells, which are located in the innermost layer of the retina. The axons of these cells converge at a point on the retina called the optic disc, where they form the optic nerve. The optic nerve is a bundle of more than a million nerve fibers that carry the electrical signals from the retina to the brain. The optic nerve exits the eye through a small opening in the back of the eye called the optic canal and then travels to the brain, where the electrical signals are processed and interpreted as visual images.

36. The pathway from the cochlea to the brain for auditory perception The pathway from the cochlea to the brain for auditory perception involves several structures and processes. After the sound waves are transmitted from the middle ear to the inner ear, they reach the cochlea. The cochlea is a spiral-shaped structure that contains fluid and thousands of tiny hair cells that are responsible for converting the sound waves into electrical signals. The electrical signals then travel along the auditory nerve, which is a bundle of nerve fibers that connect the cochlea to the brainstem. The auditory nerve fibers synapse with neurons in the cochlear nucleus, which is located in the brainstem. From the cochlear nucleus, the signals are transmitted to other brainstem nuclei, such as the superior olivary complex and the inferior colliculus. These nuclei are involved in processing the signals and integrating information from both ears. Next, the signals are transmitted to the thalamus, which is a relay station in the brain that filters and sorts sensory information before sending it to the cerebral cortex for further processing. From the thalamus, the signals are transmitted to the primary auditory cortex in the temporal lobe of the brain. The primary auditory cortex is responsible for processing basic features of sound, such as frequency and loudness. From there, the signals are transmitted to higher-order auditory areas in the cortex, where more complex aspects of sound, such as speech and music, are processed and interpreted. In summary, the pathway from the cochlea to the brain for auditory perception involves the cochlea, auditory nerve, cochlear nucleus, brainstem nuclei, thalamus, primary auditory cortex, and higher-order auditory areas in the cortex. Each structure and process plays a crucial role in the processing and interpretation of sound signals, leading to our perception of sound.

37. Comprehend the effort it takes for the body to maintain homeostasis of glucose Maintaining homeostasis of glucose in the body is essential for normal bodily functions. Glucose is the primary source of energy for the body's cells, and the levels of glucose in the blood need to be regulated to ensure that the body has a steady supply of energy. The process of maintaining glucose homeostasis involves several organs and hormones working together. When glucose levels in the blood rise, the pancreas releases insulin, a hormone that stimulates cells to take up glucose from the blood and store it as glycogen in the liver and muscles. If glucose levels in the blood fall too low, the pancreas releases glucagon, a hormone that stimulates the liver to break down glycogen into glucose and release it into the bloodstream. In addition to insulin and glucagon, other hormones, such as cortisol and epinephrine, also play a role in regulating glucose levels in the blood. These hormones are released in response to stress and can cause glucose to be released into the bloodstream to provide energy for the body's response to stress. The liver plays a crucial role in glucose homeostasis by storing and releasing glycogen in response to the levels of insulin and glucagon in the blood. The liver can also produce glucose through a process called gluconeogenesis, which involves converting non-carbohydrate sources, such as amino acids, into glucose. Muscle tissue can also store glucose in the form of glycogen and release it as needed to maintain glucose homeostasis. The process of maintaining glucose homeostasis requires coordination and communication between multiple organs and hormones in the body. Disruptions to this process can lead to conditions such as diabetes, where the body is unable to properly regulate glucose levels in the blood. Therefore, it is essential to maintain a healthy lifestyle, including a balanced diet and regular exercise, to support the body's efforts in maintaining glucose homeostasis.