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1. Homeostasis Grade 10

2. Structure of skin

3. Epidermis : This is the outermost layer of skin. It's made up of flat, dead cells that contain a protein called keratin . The epidermis doesn't have any blood vessels, making it thin and protective. It helps keep water in the body and prevents germs from getting in.

4. Dermis : The dermis is the layer between the epidermis and the hypodermis. It contains important structures like: Nerve endings that help us feel things like temperature, pain, and pressure. Sweat glands that release sweat to help cool the body and get rid of waste like urea, water, and salt. A network of blood vessels that help regulate body temperature. Hair follicles and sebaceous glands that produce oil (sebum) to keep the skin moist.

5. Hypodermis : This is the innermost layer of skin. It is made up of fat, which helps insulate the body and keep heat in. The hypodermis also stores energy.  

6. Role of Skin in Regulating Body Temperature The skin plays an important role in keeping our body temperature at a normal level, which is about 37°C (98.6°F). Here’s how it works: Temperature Receptors : The skin has special sensors (receptors) that detect changes in temperature. When the temperature goes above the set point (37°C), these receptors send messages to the brain.

7. If Body Temperature Rises : Sweat Production : Sweat glands in the skin start producing sweat. Sweat collects on the surface of the skin and evaporates, taking heat away from the body and helping to cool it down. Hair Position : In hot conditions, the muscles attached to hair relax. This allows the hair to lie flat against the skin, which helps the body lose heat.

8. Vasodilation : Blood vessels in the dermis (the middle layer of skin) widen (this is called vasodilation ). When these vessels dilate, more blood flows to the surface of the skin, allowing heat to escape more easily.

9. Role of Skin in Cold Conditions When the body temperature starts to drop below the normal level (37°C), the skin helps keep us warm in several ways: Erection of Hair : The tiny muscles at the base of hair follicles contract, pulling the hairs upright. This creates a layer of insulating air next to the skin, which helps keep warmth in. (Note: This effect is not very strong in humans compared to other animals.)

10. Vasoconstriction : Vasoconstriction : Blood vessels in the dermis (the middle layer of skin) narrow (this is called vasoconstriction ). By reducing blood flow to the skin, less heat is lost from the body. Decrease in Sweat Production : The sweat glands stop producing sweat, which helps prevent the loss of heat energy from the body.  

11. Role of Skin in Cold Conditions When the body gets cold, several processes help keep us warm: Increase in Metabolic Rate : In cold conditions, the metabolism (the body's process of converting food into energy) speeds up. This generates more heat, which is spread throughout the body via the bloodstream. The fat stored in the hypodermis (the innermost layer of skin) acts as insulation, helping to retain heat.

12. Summary of Thermoregulation When Body Temperature Falls : Blood vessels constrict (become narrower) to conserve heat. Sweat glands stop producing sweat to prevent heat loss. Shivering (involuntary muscle contractions) generates heat, warming the body. When Body Temperature Rises : Blood vessels dilate (widen), allowing more heat to escape. Sweat glands produce sweat, which cools the body as it evaporates.

13. Role of Lungs in Regulating CO₂ Levels Our body produces a lot of carbon dioxide (CO₂) during aerobic respiration , which is how our cells generate energy. Here’s how the lungs help manage CO₂ levels: CO₂ Diffusion : When blood passes through the tissues, CO₂ from the cells diffuses into the blood. In the red blood cells (RBCs), CO₂ reacts with water to form carbonic acid , thanks to an enzyme called carbonic anhydrase .

14. Bicarbonate Formation : Carbonic acid breaks down into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻). Most of these bicarbonate ions move into the blood plasma, while some CO₂ remains dissolved in the RBCs. Breathing Out CO₂ : When blood reaches the lungs, bicarbonate ions go back into the RBCs and are converted back into carbonic acid and then into CO₂. CO₂ then diffuses out of the blood into the alveoli (air sacs in the lungs) and is expelled when we breathe out.

15. Monitoring CO₂ Levels : If CO₂ levels rise in the blood, the pH (acidity) changes, and special detectors in the carotid and aortic bodies send signals to the brain. This increases the breathing rate to help expel CO₂ efficiently.

16. Role of Kidneys in Controlling Blood Composition Blood Composition : Blood is made up of two main parts: plasma and cells . Plasma is the liquid part of blood and contains a lot of water, along with important substances like: Sodium (Na⁺) Chloride (Cl⁻) Calcium (Ca²⁺) Potassium (K⁺) Nitrogenous wastes (like urea and ammonia from breaking down proteins).

17. Kidneys' Functions : The kidneys help maintain the balance of water, salts, and waste products in the blood. They do this through two main processes: filtration and reabsorption . Filtration : Blood flows into the kidneys, where tiny structures called nephrons filter the blood. During filtration, water, solutes, and waste products pass through, while larger cells and proteins stay in the blood.

18. Reabsorption : After filtration, the kidneys reabsorb the substances the body still needs, like water and important ions (sodium, calcium, etc.). This process ensures that the right balance of fluids and electrolytes is maintained in the blood.

19. The Urinary System Kidneys : The kidneys are two reddish-brown, bean-shaped organs located at the back of the abdominal cavity, one on each side of the spine. They are positioned just above the waistline. Each kidney has a special area called the hilus on its concave surface, which faces the spine. This is where the renal artery, renal vein, nerves, and ureters connect.

20. Ureters : The ureters are narrow tubes that transport urine from the kidneys to the urinary bladder. Urinary Bladder : The urinary bladder is a thin-walled, muscular bag located at the bottom of the abdominal cavity, in front of the rectum. It stores urine until you are ready to go to the bathroom.

21. Urethra : The urethra is a tube that carries urine from the bladder out of the body. It runs down from the bladder and opens to the outside through the urinary opening. Urine : Urine is the liquid waste that the kidneys produce. It travels from the kidneys, through the ureters, and is stored in the bladder until it is expelled through the urethra.

22. Structure of the Kidney Kidney Location : Each kidney is surrounded by a membrane called the peritoneum , which contains a fluid that helps reduce friction

23. Parts of the Kidney : The kidney has three main parts: Cortex : This is the outer, dark brown layer that is protected by a fibrous capsule. Medulla : This is the inner, lighter layer that contains cone-shaped structures called renal pyramids . A human kidney typically has 12 to 16 pyramids. Pelvis : This is the funnel-shaped space that connects the kidney to the ureter, allowing urine to flow out.

24. Nephrons : Inside the medulla, there are tiny structures called nephrons , which are the basic functional units of the kidney. Nephrons are responsible for filtering blood and producing urine.

25. Structure of Nephron Nephron Parts : Each kidney has over a million nephrons, and each nephron has four main parts: Bowman's Capsule : This surrounds the glomerulus (a cluster of tiny blood vessels). Proximal Convoluted Tubule : This is the first tubule that processes the filtered fluid. Loop of Henle : This part helps concentrate urine. Distal Convoluted Tubule : This is the final tubule before urine enters the collecting duct.

26. Blood Supply : Nephrons are surrounded by blood vessels connected to the renal artery and renal vein . Blood is filtered in the glomerulus and then processed in the nephron

27. Role of Kidney in Urine Formation Urea Formation : Urea is produced in the liver when proteins are broken down. Here’s how it works: The liver cannot store proteins, so it breaks down excess amino acids for energy. During this process, an amino group (NH₂) is removed from the amino acids, a process called deamination .

28. This amino group is converted into ammonia (NH₃) , which is toxic if it builds up in the body. The liver quickly converts ammonia into urea , a less harmful substance. Urea is then carried by the blood to the kidneys, where it is excreted in urine. A small amount of urea is also lost in sweat.