Histology 1 Flashcards
What is the circulatory system composed of? (2)
- Cardiovascular system
* Lymphatic system
What are the roles of the cardiovascular system? (5)
- Transport of oxygen and nutrients to tissues
- Transport of CO2 and other metabolic waste from the tissues
- Temperature regulation
- Distribution of hormones and immune cells
- Reproductive function in males - penile erection (lol)
Where is the majority of blood at rest?
Peripheral veins (~60%)
What are the blood vessel layers? (3)
- Inner layer - tunica intima
- Middle layer - tunica media
- Outer layer - tunica adventitia
What is the tunica intima? What is it supported by?
- Single layer of squamous epithelial cells termed endothelial cells
- supported by a basal lamina and a thin layer of connective tissue
What is tunica media?
Predominately smooth muscle - thickness of this layer varies tremendously
What is tunica adventitia?
Made up of supporting connective tissue
What is all vasculature lined by?
Endothelial cells
In which vessels is tunica media lost?
Capillaries
What does tunica adventitia blend with?
Surrounding connective tissue
What separates the tunica intima and tunica media layers? Tunica media and tunica adventitia?
- Internal elastic membrane
* External elastic membrane
How are elastic fibres visualised in microscopy?
- Not stained using most common stains (including H&E) but can be visualized with special stains e.g. black
Why are the largest arteries (e.g. aorta) termed elastic arteries?
Have many sheets of elastic fibres in tunica media to provide elastic recoil (smooth muscle replaced with elastic tissue)
What is the purpose of elastic arteries?
- Stops blood pressure skyrocketing during systole
* Maintains blood pressure in diastole
In large vessels, which areas can obtain nutrients from the lumen? Therefore, how do other parts obtain nutrients?
- Only inner part of wall
* Will have own vascular supply (Vasa vasorum)
What is vascular supply to large vessels called?
Vaso vasorum
Describe the layers of arterioles? Diameter? Function?
- Only 1-2 layers of smooth muscle in their tunica media and almost no adventitia
- 30-200 um
- Important in controlling blood flow to a tissue
Describe the layers of capillaries? Diameter?
- Only composed of endothelial cells and a basal lamina
* 4-8 um
What do capillaries often contain just outside the basal lamina? What are these?
- Pericytes
* Connective tissue cells that have contractile (and stem cell) properties
What are the 3 types of capillary? What are they?
- Continuous - endothelial cells form continuous wall
- Fenestrated - have 50mm pores in wall
- Discontinuous (sinusoidal) - lack basal lamina and have gaps which macromolecules and cells can pass
Where are the 3 types of capillary found?
- Continuous - muscle, connective tissue, lung, skin, nerve
- Fenestrated - gut mucosa, endocrine glands, glomeruli of the kidney
- Discontinuous (sinusoidal) - liver, spleen and bone marrow
Explain the composition of microvascular networks?
- Small arterioles connect to a postcapillary venule through a network of metarterioles (smallest arteriole before reaching capillaries), thoroughfare channels and capillaries
What is the purpose of pre-capillary sphincters? What are they composed of?
- Control flow of blood through the network
* Smooth muscle
Explain the layers of post-capillary venules? Diameter? Function?
- Endothelial cell-lined and contain a thin layer of connective tissue and occasional pericytes
- 10-30 um
- Important sites for exchange, e.g. cells moving into the tissue in inflammation
When are post-capillary venules called venules? When are venules called veins?
- Once vessel begins to acquire intermittent smooth muscle cells in tunica media layer
- Called veins once have a few layers of smooth muscle cells
What are the layers of veins? What is the difference between layers of vein and artery?
- Tunica intima and relatively thin tunica media with only a few layers of SM
- Tunica media way thinner than would be found in a muscular artery
What layers do the largest veins have?
- Thick tunica adventitia which incorporates bundles of longitudinally oriented smooth muscle
Why do veins contain most of the blood in the body?
Veins are flexible and can accommodate expansion
What do most small to medium veins have?
Valves that are inward extensions of the tunica intima
What are the layers of the heart? (3)
- Endocardium - inner layer
- Myocardium - middle layer
- Epicardium - outer layer
Name labelled structures of heart (pic)
A - Endocardium B - Myocardium C - epicardium D - pericardium E - adipose F - visceral serous pericardium G - parietal serous pericardium H - fibrous pericardium I - pericardial cavity
What does endocardium line?
Entire inner surface of the heart including valves
What is the structure of the endocardium?
- Endothelium
- Basal lamina
- Thin layer of collagen fibres
- Layer of denser connective tissue
- Subendocardium (only in some areas) of loose connective tissue containing small blood vessels and nerves and branches of the impulse conducting system
Where is subendocardium particularly present?
Interventricular septum
What are found in subendocardium?
Purkinje fibres contained within conducting cells
What is the structure of the myocardium? (2)
- Bundles and layers of contractile cardiac muscle fibres
* Individual muscle fibres surrounded by connective tissue with a rich network of capillaries
What are features of cardiac muscle cells? (3)
- Striated
- Single central nucleus
- Intercalated discs
What are the functions of intercalated discs? (2)
- Join cells end-to-end to prevent separation during contraction
- Spread of electrical activity
What is the structure of the epicardium? (3)
- On surface of heart: single layer of flattened epithelium called mesothelium (also on lung surface)
- Basal lamina
- Fibroelastic connective tissue - also adipose tissue in some places
What is the purpose of adipose tissue present in epicardium?
Coronary vessels typically embedded in this
What are the 2 parts of the pericardium? What are they made up of?
- Fibrous pericardium - tough fibrocollagenous connective tissue
- Serous pericardium - layer of simple squamous epithelium (mesothelium) backed by basal lamina and connective tissue
What is the serous pericardium further split into? (2)
- Parietal serous pericardium (in contact with fibrous pericardium)
- Visceral serous pericardium (in contact with heart)
What are the 2 mesothelial (SEROUS) layers seperated by? What is the function of pericardial fluid?
- Pericardial cavity which contains small volume (15-50ml) of pericardial fluid
- Provides lubrication for heart movement
What is the fibrous skeleton of the heart formed by? What is the purpose of the fibrous skeleton? (3)
- Thick bands of fibrous connective tissue around the heart valves, between the atria, and between the ventricles
- Supports valves
- Provides attachment for cardiac muscle fibres
- Prevents ectopic spread of electricity from atria to ventricles
What is the structure of the heart valves?
- Outer endothelial layer with basal lamina
- Layer of collagen and elastin fibres
- Core of dense connective tissue called the lamina fibrosa in continuity with the fibrous skeleton
How are leaflets of mitral and tricuspid valves prevented from refluxing into atrium during ventricular contraction?
Anchored to papillary muscles in wall of the ventricle by chordae tendineae which merge with the lamina fibrosa to form touch anchor
Do the heart valves contain blood vessels?
No
What is the lamina fibrosa?
The core of a heart valve and is dense irregular connective tissue that is continuous with the fibrous skeleton of the heart
What is the valve covered on bot sides by?
Endothelium
What are the 3 types of cardiac muscle cells (myocytes)?
- Contractile cells (99%)
- Pacemaker cells
- Conducting cells
What are pacemaker and conducting cells?
Modified cardiac muscle cells
How do pacemaker cells differ from contractile cardiac myocytes? (4)
- Considerably smaller (4-8um)
- Embedded in more extensive matrix of connective tissue
- Very few irregularly-arranged myofibrils
- Little glycogen and no proper T-tubule system
Why do pacemaker cells appear pale histologically?
Due to scarceness of organelles within them
What is the purpose of the AV tunnel of the fibrous cardiac skeleton?
Electrical activity passes through tunnel just below AV valve into interventricular conduction
How does fibrous cardiac skeleton electrically isolate atria from the ventricles?
No excitation passes through the non-conducting tissue of skeleton
What is the difference between conducting cells (purkinje fibres) and normal cardiac muscle cells? (6)
- Much larger
- Found in subendocardial layer deep to endocardium
- Have abundant glycogen
- No T-tubules
- No intercalated discs
- Sparse actin and myosin filaments
What do purkinje fibres/conducting cells appear like histologically? Why?
- Very pale
* Sparse actin and myosin filaments only found at the periphery of the cell
How do purkinje fibres distribute excitatory activity?
Such that ventricular contraction occurs form inferior to superior
What does lymphatic system consist of? What tissues do not have lymphatic drainage?
- Lymphatic vessels that drain tissue fluid, eventually returning it to veins in the base of the neck
- Bone and brain
What is a significant difference between lymphatic circulation and systemic circulation? What is tissue fluid (interstitial fluid) composed of? (4)
- Lymphatic circulation is not a complete circuit - lymphatics are blind-ending
- Ions, lipids, proteins and cells
Where does excess interstitial fluid drain?
Most excess interstitial fluid returns to capillaries and venous vessels, but a portion returns to the circulatory system by entering lymphatic vessels
What does lymph pass through on the way to the root of the neck? What is the purpose of this?
- Lymph nodes
* Immunological surveillance
How is flow produced in lymphatic vessels? (3)
No central pump so..
- Hydrostatic pressure in tissue
- Compression of vessels by voluntary muscle
- Valves in the vessels
