Histological techniques ( A lecture for 7th semester students).pptx

Histological techniques ( A lecture for 7th semester students).pptx

1. Histological techniques Dr Showkat Ahmad Wani

2. Histological Techniques The steps by which we prepare tissues so that we can study them under a microscope .

3. What is Histology? Histology means the study of tissues under a microscope. Just as a doctor studies a patient to find out what’s wrong, a histologist studies tissues to understand their structure and function , and also to detect diseases . But before we can look at a tissue under the microscope, we must prepare it properly — and that’s what histological techniques are about.

4. Why do we need histological techniques? Tissues are soft and delicate. If we try to cut and observe them directly, they will break or rot . So, we must: Preserve them, Make them firm , and Stain them, so we can see different parts clearly.

5. Main Steps in Histological Techniques Let’s understand the steps one by one:

6. 1. Fixation Purpose: To preserve the tissue and prevent decay. Common Fixative: Formalin (10% formaldehyde). How it works: It “fixes” the proteins and cells in place, keeping their structure as natural as possible. 🧴 Think of it like pickling vegetables — we preserve them to stop rotting.

7. 2. Dehydration Purpose: To remove water from the tissue. Why? Because the next step (embedding) uses wax, and wax doesn’t mix with water. How it’s done: The tissue is passed through increasing concentrations of alcohol (like 70%, 90%, and 100%).

8. 3. Clearing Purpose: To remove alcohol and make the tissue transparent. Common chemical used: Xylene . It prepares the tissue for embedding in wax. 👓 Clearing makes tissues look clear, like glass.

9. 4. Embedding Purpose: To make the tissue firm for cutting. The tissue is placed in molten paraffin wax , which later hardens. This forms a block that can be cut easily. 🧈 Imagine setting jelly in a mould — once it cools, it becomes firm.

10. 5. Sectioning Purpose: To cut thin slices of tissue. Tool used: Microtome (a machine that cuts very thin sections — as thin as 5 micrometers!). The thin slices are placed on glass slides . ✂️ It’s like cutting paper-thin slices of tissue.

11. 6. Staining Purpose: To give color to the tissue parts, since most are naturally colorless. Common stains: Hematoxylin – stains the nucleus blue or purple Eosin – stains the cytoplasm pink Together called H&E staining — the most common stain in histology.

12. 7. Mounting Purpose: To protect the stained tissue and make it permanent. A thin glass cover slip is placed over the tissue using a mounting medium . 🧫 Now the slide is ready to be viewed under the microscope.

13. Summary Chart Step Purpose Common Chemical/Tool Fixation Preserve tissue Formalin Dehydration Remove water Alcohol Clearing Make tissue transparent Xylene Embedding Make tissue firm Paraffin wax Sectioning Cut thin slices Microtome Staining Give color Hematoxylin & Eosin Mounting Protect tissue DPX, coverslip

14. Remember: The goal of histological techniques is to prepare tissue so it can be seen clearly under the microscope without losing its natural structure. Example : If we take a piece of liver and prepare it using these steps, we can clearly see hepatocytes , nuclei , and blood sinusoids under the microscope.

15. Thank you