1. VAN-504, Lecture- 01
General Histology: Structure of animal cell and basic tissues and their functional activity

2. Histology
The term histology, is derived from the Greek histos, meaning tissue (web) and logia, knowledge
It is, in the strict sense, the knowledge, or science, of tissues whether they are of plants or animals
is the study of the microscopic anatomy of cells and tissues of plants and animals
It is performed by examining a thin slice (section) of tissue under a light or electron microscope

3. Veterinary Histology: Is the science that focuses on the detailed morphology of tissues of domestic animals with the aid of microscope and correlates specific structures with function
Veterinary Microanatomy: Involves the examination and architectural description of the microscopic anatomy of normal cells of the body and all their contents and products

4. HISTORY
Robert Hooke was the first person to observe cells in He looked at thin slices of cork under a very simple microscope. The cork appeared as little boxes which he called cells
In 1883 Mathias Schleiden and Theodor Schwann proposed that all plants and animals were composed of cells which were the basic building blocks of life
In 1855 Rudolf Virchow stated that new cells arise from the division of pre-existing cells and that chemical reactions needed for life occurred inside the cell
All this work led to the formation of the cell theory

5. LEVELS OF ORGANIZATION
Tissues
Organs
Organ
Systems
Organism
Cells
Cells
Tissues
Organs
Organ Systems
Organism

6. Cell: Is defined as the smallest basic structure of higher organisms capable of independent existence
Tissue: Is a group of cells of similar function and origin that form functional units
Organ: An organ represent an even greater measure of complexity and is composed of various tissues
System: At an even higher level of organization: An organ system composed of several organs (such as the gastrointestinal system, respiratory system, cardiovascular system, endocrine system)
Organism: An organism can be seen to be formed of different levels of organization, with increasing levels of complexity and each of which plays important roles in the physiological homeostasis of the body

7. Histological Terms
The photographing of stained cells is called Histography or Photomicrography
Histopathology is the microscopic study of diseased tissue
The trained scientists who perform the preparation of histological sections are Histotechnicians, Histology Technicians, Histology Technologists.
Their field of study is called Histotechnology

8. Source of Tissue Histological examination of tissues starts
with surgery, biopsy or autopsy (or
necropsy, in the case of animal tissues).
Biopsy is an examination of tissue taken from a living body
Autopsy is an examination of post-mortem tissue
Necropsy is an examination of tissue taken from dead animal

9. Histological Classification of Animal Tissues
There are four basic types of tissues:
Epithelial tissue
Muscle tissue
Connective tissue
Nervous tissue

10. Epithelial tissue
A sheet of aggregated cells of a similar type tightly adhered to each other, constitutes the external and internal surfaces of the body
Epithelium: the lining of glands, bowel, skin and some organs like the liver, lung, kidney,
Endothelium: the lining of blood and lymphatic vessels,
Mesothelium: the lining of pleural, and pericardial spaces,

11. CONNECTIVE TISSUE
Connective tissue is responsible for providing structural support for the tissues and organs of the body.
This mechanical function is important in maintaining the form of the body, organs and tissues.
Connective tissue is composed of:
cells
extracellular matrix.

12. MUSCLE TISSUE
Muscle tissue is characterized by its well-developed properties of contraction
 Muscle is responsible for the movements of the body and the various parts of the body
Muscle develops from embryonic mesoderm Muscle is classified into 3 categories according to morphology and physiological function:
Skeletal Muscle
Cardiac Muscle
Smooth Muscle

13. NERVOUS TISSUE Nervous tissue consists of two groups of cell types:
Nerve cells (Neurons)
Neuroglia.
nervous tissue is derived from embryonic neuroectoderm
The nervous system is divided anatomically into:
Central Nervous System (CNS), consisting of the brain and spinal cord.
Peripheral Nervous System (PNS), consisting of nerve fibers, aggregates of nerve cells and glia and ganglia.

14. Cell Prokaryotic - bacteria, blue-green algae
Eukaryotic - plants, animals, fungi, many unicellular organisms
Both cell types:
- have DNA,
- are membrane bound,
- have ribosomes,
- have similar basic metabolism
Eukaryotic cells:
- larger (~1000X),
- more complex DNA,
- have a nuclear and organelle membranes,
- have cytoskeleton

15. Comparing Prokaryotic and Eukaryotic Comparing Prokaryotic and Eukaryotic ls
All cells have several basic features in common
They are bounded by a plasma membrane
They contain a semi-fluid substance called the cytosol
They contain chromosomes
They all have ribosomes
Eukaryotic cells
Contain a true nucleus, bounded by a membranous nuclear envelope
Are generally quite a bit bigger than prokaryotic cells
The logistics of carrying out cellular metabolism sets limits on the size of cells
Have extensive and elaborately arranged internal membranes, which form organelles
Prokaryotic cells
Do not contain a nucleus
Have their DNA located in a region called the nucleoid

16. Prokaryotic cells

17. Eukaryotic Cell

18. Structure of the plasma membrane
Functions as a selective barrier
Allows sufficient passage of nutrients and waste
Outside of cell
Inside of cell
Hydrophilic
region
Hydrophobic
Structure of the plasma membrane
Phospholipid
Proteins
TEM of a plasma
membrane. The
(a)
0.1 µm

19. The fluid mosaic model of membrane structure
Cellular membranes are fluid mosaics of lipids and proteins
Phospholipids
Are the most abundant lipid in the plasma membrane
Are amphipathic, containing both hydrophobic and hydrophilic regions
The fluid mosaic model of membrane structure
States that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it

20. Hydrophobic region of protein
In 1972, Singer and Nicolson
Proposed that membrane proteins are dispersed and individually inserted into the phospho-lipid bi-layer
Phospholipid
bilayer
Hydrophobic region
of protein
Hydrophobic region of protein

22. Lipid soluble substances can enter and leave the cell by passive diffusion following concentration gradients

23. Substances can also cross the membranes without energy expenditure via osmosis = solvent molecules (usually H20) move across a semi-permeable membrane due to osmotic pressure

24. Cell
Facilitated or carrier-mediated diffusion occurs with molecules that are not normally fat soluble, but become so when combined with a carrier substance allowing entry or exit from the cell

25. Active transport is the movement of substances against a concentration or electrochemical gradient and usually requires energy expenditure by the cell

26. Large molecules or entire cells can enter the host cell by
endocytosis either via pinocytosis or phagocytosis and exit
the cell via exocytosis

27. Nucleus
The nucleus is made up of DNA [deoxyribonucleic acid], and RNA [ribonucleic acid], and is involved in cell reproduction and metabolic activities
Nucleoli may be present in resting cells and are sites of ribosomal RNA production
The nucleus is surrounded by a nuclear membrane containing pores and continuous with the endoplasmic reticulum in some areas

28. DNA is made up of chains of nucleotides and form the basic element of genes which determine all of our inherited characteristics
Nucleotides consist of a sugar molecule - deoxyribose bonded with a phosphate group and a nitrogenous base
Nitrogenous bases can be either adenine, guanine, cytosine or thymine

29. DNA is usually found in double, complementary strands that are held together by hydrogen bonds between the nitrogenous bases
Adenine binds with thymine, cytosine binds with guanine
When the DNA is not replicating, these strands form a spiral or double helix

30. During DNA
replication, the
complementary
strands separate
and enzymes
known as
polymerases
add new bases
that are identical
to the original
opposite strand

31. Mitosis, or cell division, produces two genetically identical cells

32. Endoplasmic Reticulum

33. Endoplasmic Reticulum (E.R.)
Transports materials and sends messages to all parts of the cell
Two types: smooth and rough (has ribosomes)
Location: attaches from cell membrane to nuclear membrane
Rough E.R

35. Electron microscope pictures showing the rough ER and ribosomes producing proteins

37. Golgi apparatus
is found close to the nucleus and endoplasmic reticulum.
It’s function is to receive, sort and process the biomolecules it receives from the ER and resecrete them.
Enzymes in golgi complex transfer carbohydrate units to proteins to form of glycoporoteins, this determines the ultimate destination of proteins.
Golgi is the major site for the synthesis of new membrane, lysosomes and peroxisomes.
It plays two major roles in the membrane synthesis:

39. Golgi Apparatus

40. Mitochondria
Mitochondria are used for aerobic respiration and production of energy (ATP) for the for proper functioning of the cells metabolic processes.

41. Mitochondria

42. Lysosomes
Lysosomes are full of enzymes that break down fats, protein and carbohydrates into their smallest elements to be used by the mitochondria for energy
Vacuoles are often found in the cytoplasm and assist in getting rid of water and waste products from the cell

43. CYTOSKELETON

44. Microtubules provide support for the cell known as
the cytoskeleton to help the cell keep its shape
and control flow of elements through the cell.
Microtubules also make up cilia and flagella that are hair-like surface projections used to move the cells themselves or material around the outside the cells.
Centrioles are bundles of microtubules that
assist in separation of the chromosomes
during mitosis when they form into
mitotic spindles.

45. Tissues
Cells bound together and serving a specific function are called tissues and include
- epithelium,
- connective tissue,
- muscle tissue,
- nerve tissue.
Epithelium: consists of sheets of cells that have a basal lamina and an unattached or free edge. It is typically found lining cavities, blood vessels, gland ducts and hollow organs.

46. Tissues Epithelium serves different functions depending on its type
and location but may be for
- protection,
- absorption,
- secretion or
- to facilitate movement of substances over its free surface

47. Connective tissue
Connective tissue is found throughout the body and contains a variety of different cell types, depending on its location
Dense and loose connective tissue contains fibroblasts and collagen fibers which provide elasticity to the tissue

48. Connective tissue

49. Connective tissue
Adipose tissue contains adipocytes which store fat for metabolism and is primarily white. Brown fat is in many species but the greatest amount is found in species that hibernate and it is thought to have a role in maintaining body temperature by producing heat.

50. Connective Tissues
Cartilage contains chondrocytes that are embedded in a semi-rigid matrix. The number of fibers and density of the matrix determines whether it is hyaline cartilage, elastic cartilage, or fibrocartilage.

51. Connective Tissues
Bone is made up of osteocytes and ground substance that consists of calcium phosphate. The ends of long bones contain spongy or cancellous bone while the shaft is compact bone that surrounds the medullary cavity containing the bone marrow

52. Connective Tissues
The cells found within connective tissue can be fixed as seen with fibroblasts, chondrocytes, osteocytes, and adipose cells.
They can also be wandering, usually coming from the blood, as seen with eosinophils, neutrophils, lymphocytes, monocytes, and mast cells.

53. Muscle Tissues
Muscle cells can either be smooth or striated, depending on their function and appearance under a microscope. Smooth muscle is found in most of the our internal organs and exhibits involuntary rhythmic and tonic contractions

54. Muscle Tissues
Striated muscle can be either skeletal muscle, that contracts voluntarily, or cardiac muscle that contracts involuntarily.

55. Nervous Tissues
Nerve tissue is made up of neurons that are cells characterized by a nucleated cell body, dendrites, and an axon. Nerves respond to stimuli by polarizing and depolarizing by varying the concentration of sodium and potassium ions inside the cell.

56. Nervous Tissues
Many nerves are covered with a myelin sheath that speeds the conduction of the impulses down the axon. The myelin is made from part of an oligodendrocyte cell that wraps around the axon and has gaps in it called nodes of Ranvier.

57. Nervous Tissues
The axons end either in synapses with other nerve cells, or in motor end plates, innervating muscle cells. The end releases neurotransmitters which are chemicals that stimulate the next nerve or muscle to respond.