Arteriole, venule and capillary histology

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Arteriole, venule and capillary histology

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Introduction to the cardiovascular system
Anatomy of the heart
Anatomy of the coronary circulation
Anatomy clinical correlates: Heart
Anatomy of the superior mediastinum
Anatomy of the inferior mediastinum
Anatomy clinical correlates: Mediastinum
Development of the cardiovascular system
Fetal circulation
Cardiac muscle histology
Artery and vein histology
Arteriole, venule and capillary histology
Cardiovascular system anatomy and physiology
Lymphatic system anatomy and physiology
Coronary circulation
Blood pressure, blood flow, and resistance
Pressures in the cardiovascular system
Laminar flow and Reynolds number
Resistance to blood flow
Compliance of blood vessels
Control of blood flow circulation
Microcirculation and Starling forces
Measuring cardiac output (Fick principle)
Stroke volume, ejection fraction, and cardiac output
Cardiac contractility
Frank-Starling relationship
Cardiac preload
Cardiac afterload
Law of Laplace
Cardiac and vascular function curves
Altering cardiac and vascular function curves
Cardiac cycle
Cardiac work
Pressure-volume loops
Changes in pressure-volume loops
Physiological changes during exercise
Cardiovascular changes during hemorrhage
Cardiovascular changes during postural change
Normal heart sounds
Abnormal heart sounds
Action potentials in myocytes
Action potentials in pacemaker cells
Excitability and refractory periods
Cardiac excitation-contraction coupling
Electrical conduction in the heart
Cardiac conduction velocity
ECG basics
ECG rate and rhythm
ECG intervals
ECG QRS transition
ECG axis
ECG normal sinus rhythm
ECG cardiac infarction and ischemia
ECG cardiac hypertrophy and enlargement
Baroreceptors
Chemoreceptors
Renin-angiotensin-aldosterone system
Arterial disease
Angina pectoris
Stable angina
Unstable angina
Myocardial infarction
Prinzmetal angina
Coronary steal syndrome
Peripheral artery disease
Subclavian steal syndrome
Aneurysms
Aortic dissection
Vasculitis
Behcet's disease
Kawasaki disease
Hypertension
Hypertensive emergency
Renal artery stenosis
Coarctation of the aorta
Cushing syndrome
Conn syndrome
Pheochromocytoma
Polycystic kidney disease
Hypotension
Orthostatic hypotension
Abetalipoproteinemia
Familial hypercholesterolemia
Hypertriglyceridemia
Hyperlipidemia
Chronic venous insufficiency
Thrombophlebitis
Deep vein thrombosis
Lymphedema
Lymphangioma
Shock
Vascular tumors
Human herpesvirus 8 (Kaposi sarcoma)
Angiosarcomas
Truncus arteriosus
Transposition of the great vessels
Total anomalous pulmonary venous return
Tetralogy of Fallot
Hypoplastic left heart syndrome
Patent ductus arteriosus
Ventricular septal defect
Atrial septal defect
Atrial flutter
Atrial fibrillation
Premature atrial contraction
Atrioventricular nodal reentrant tachycardia (AVNRT)
Wolff-Parkinson-White syndrome
Ventricular tachycardia
Brugada syndrome
Premature ventricular contraction
Long QT syndrome and Torsade de pointes
Ventricular fibrillation
Atrioventricular block
Bundle branch block
Pulseless electrical activity
Tricuspid valve disease
Pulmonary valve disease
Mitral valve disease
Aortic valve disease
Dilated cardiomyopathy
Restrictive cardiomyopathy
Hypertrophic cardiomyopathy
Heart failure
Cor pulmonale
Endocarditis
Myocarditis
Rheumatic heart disease
Pericarditis and pericardial effusion
Cardiac tamponade
Dressler syndrome
Cardiac tumors
Acyanotic congenital heart defects: Pathology review
Cyanotic congenital heart defects: Pathology review
Atherosclerosis and arteriosclerosis: Pathology review
Coronary artery disease: Pathology review
Peripheral artery disease: Pathology review
Valvular heart disease: Pathology review
Cardiomyopathies: Pathology review
Heart failure: Pathology review
Supraventricular arrhythmias: Pathology review
Ventricular arrhythmias: Pathology review
Heart blocks: Pathology review
Aortic dissections and aneurysms: Pathology review
Pericardial disease: Pathology review
Endocarditis: Pathology review
Hypertension: Pathology review
Shock: Pathology review
Vasculitis: Pathology review
Cardiac and vascular tumors: Pathology review
Dyslipidemias: Pathology review
Sympatholytics: Alpha-2 agonists
Adrenergic antagonists: Presynaptic
Adrenergic antagonists: Alpha blockers
Adrenergic antagonists: Beta blockers
ACE inhibitors, ARBs and direct renin inhibitors
Thiazide and thiazide-like diuretics
Calcium channel blockers
cGMP mediated smooth muscle vasodilators
Class I antiarrhythmics: Sodium channel blockers
Class II antiarrhythmics: Beta blockers
Class III antiarrhythmics: Potassium channel blockers
Class IV antiarrhythmics: Calcium channel blockers and others
Lipid-lowering medications: Statins
Lipid-lowering medications: Fibrates
Miscellaneous lipid-lowering medications
Positive inotropic medications
Cardiomyopathies: Clinical
Congenital heart defects: Clinical
Valvular heart disease: Clinical
Infective endocarditis: Clinical
Pericardial disease: Clinical
Chest trauma: Clinical
Hypertension: Clinical
Pulmonary hypertension
Aortic aneurysms and dissections: Clinical
Raynaud phenomenon
Peripheral vascular disease: Clinical
Heart failure: Clinical
Coronary artery disease: Clinical
Deep vein thrombosis and pulmonary embolism: Pathology review
Fascia, vessels and nerves of the upper limb
Vessels and nerves of the forearm
Vessels and nerves of the hand
Anatomy of the abdominal viscera: Blood supply of the foregut, midgut and hindgut
Fascia, vessels, and nerves of the lower limb
Vessels and nerves of the gluteal region and posterior thigh
Anatomy of the popliteal fossa
Ventilation
Ventilation-perfusion ratios and V/Q mismatch
Gas exchange in the lungs, blood and tissues
Oxygen binding capacity and oxygen content
Oxygen-hemoglobin dissociation curve
Carbon dioxide transport in blood
Trypanosoma cruzi (Chagas disease)
Yellow fever virus
Rickettsia rickettsii (Rocky Mountain spotted fever) and other Rickettsia species
Arteriovenous malformation
Cerebral circulation

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The circulatory system consists of two functional parts, the lymphatic system and the blood circulatory system.

The microvasculature is part of the blood circulatory system and consists of the arterioles, capillaries, and venules.

This is the portion of the circulatory system that’s responsible for the exchange of gases, nutrients, fluids, and metabolic waste.

The majority of this exchange occurs in the capillaries.

The arterioles are continuations of the small muscular arteries that can constrict in order to control the amount of blood that flows into the capillary beds.

There are also muscular precapillary sphincters between the arterioles and capillaries called precapillary sphincters, that also help control how much blood flows to the capillary beds.

The capillaries drain the blood into the postcapillary venules, then the collecting venules, and finally the small muscular venules.

The small muscular venules gradually increases in diameter and eventually drain into small veins.

Alright, this image is an example of an arteriole from the abdominal mesentery.

Similar to most blood vessels, the arteriolar wall has three main layers, the tunica intima, tunica media, and tunica externa.

The tunica intima consists of an internal elastic membrane or lamina and an inner lining of flat endothelial cells with round nuclei.

The tunica media consists of 1 to 2 layers of circularly arranged smooth muscle.

The tunica externa surrounding the smooth muscle is a very thin layer of fibrous tissue that can be difficult to identify in images like this.

Here’s an example of a smaller arteriole.

We can see 3 nuclei from endothelial cells and two smooth muscle nuclei.

In smaller arterioles like this one, the internal elastic lamina is not present.

After the arterioles, blood flows into the capillaries, which are the blood vessels with the smallest diameter in the body.

The walls of the capillaries are composed of only a single layer of endothelium surrounded by a very thin basement membrane.

There are a few types of capillaries, but the most common type is the continuous capillary.

These capillaries have many tight junctions joining the endothelial cells together in order to form a very thin tube.

As a result, larger molecules and proteins leaving or entering the capillary are regulated by the endothelial cells, since any substances that leave the capillary will have the pass through the layer of endothelial cells.

This image shows a cross-section of a few continuous capillaries surrounded by adipose tissue.

The cytoplasm of the endothelial cells are difficult to see with light microscopy, but we can still see the nuclei of the endothelial cells in the upper left and upper right capillaries stained dark purple, as well as a single red blood cell or RBC in each of their lumens.

In general, the diameter of the capillaries are about the same as a single RBC, which can be a useful tool to gauge the size of surrounding structures in an image, since RBCs normally have a diameter of 6 to 8 µm.

In longitudinal sections of capillaries, the nuclei will look more elongated compared to cross-sections.

Occasionally, you can also see flattened supportive cells that surround the capillary called pericytes.

In this image, we can see a pericyte along the bottom of the capillary.

Fenestrated capillaries also have tight junctions, but perforations or fenestrations through the endothelial cells allow greater exchange across the endothelium.

Similar to the continuous capillaries, the basement membrane is also continuous with no perforations.

Fenestrated capillaries are found in organs where molecular exchange with the blood is important, such as endocrine organs, intestinal walls, and choroid plexus.

Summary

Arterioles, venules, and capillaries are all small blood vessels that play an important role in the cardiovascular system. Each type of vessel has a different structure and function, but they all work together to transport blood throughout the body.

Arterioles are the smallest arteries in the body and they are responsible for regulating blood flow by constricting or dilating in response to various signals. Venules are small veins that collect blood from the capillaries and return it to the larger veins, whereas capillaries form a network between arterioles and venules, and provide a path for nutrients, oxygen, carbon dioxide, and wastes exchange between the bloodstream and tissues.

The histology of each type of vessel is different, but all are lined with a layer of endothelial cells. The smooth muscle cells that make up the walls of arterioles and venules are arranged in layers, while the capillaries only have a single layer of endothelial cells.

Sources

  1. "Histology. A Text and Atlas" Wolters Kluwer (2018)
  2. "Wheater's Functional Histology" Churchill Livingstone (2013)
  3. "Junqueira's Basic Histology: Text and Atlas, Fourteenth Edition" McGraw-Hill Education / Medical (2015)
  4. "Robbins Basic Pathology" Elsevier (2017)
  5. "Diagnostic Immunohistochemistry" Elsevier (2021)
  6. "Cytology" Saunders (2013)
  7. "Cytology" Saunders (2013)
  8. "Liver Sinusoidal Endothelial Cell: An Update" Seminars in Liver Disease (2017)
  9. "Vascular Endothelial Cell Biology: An Update" International Journal of Molecular Sciences (2019)