Histology - Circulatory

Front 1

1.What characterizes the tunica intima of the blood vessels?

Back 1

Endothelial cells (simple squamous epithelium) over a basal lamina.
Subendothelial layer: Connective tissue + smooth muscle cells longitudinally arranged.

Front 2

1.What characterizes the tunica media of the blood vessels?

Back 2

Smooth muscle cells creating concentric spiral layers.
Intercellular substance: Reticular fibres and proteoglycans.
Internal elastic lamina: In arteries, made of elastin and with fenestrae (holes).
External elastic lamina: In larger arteries.

Front 3

1.What characterizes the tunica adventitia of the blood vessels?

Back 3

Longitudinally oriented collagen and elastic fibres; peripherally they blend with the surrounding connective tissue

Front 4

1.What particularities have the tunica media and tunica adventitia in the capillary vessels?

Back 4

Tunica media - In the capillaries and postcapillary venules it is represented by the pericytes.
Tunica adventitia - In the capillaries it is represented by a layer of reticular fibres.

Front 5

1.What is the vasa vasorum?

Back 5

Vessels of the vessels present in large vessels, usually at the adventitia and outer parts of the media. They also include lymphatic vessels.

Front 6

1.What is the vasa nervorum and what is the nature of most of the nerves that act upon the blood vessels?

Back 6

Nerves of the vessels. Unmyelinated sympathetic fibres with actions over smooth muscle; they release norepinephrine producing vasoconstriction.

Arteries in skeletal muscle have also cholinergic (vasodilator) nerves.

Front 7

1.What defines the capillary vessels?

Back 7

Single layer of endothelial cells elongated on the direction of blood flow, with diameter of 7 – 9 µm and length of 0.25 – 1 mm.
All those related with permeability
Metabolic: Activation: angiotensin I to II
Inactivation: conversion of bradykinin, serotonin, prostaglandins and others to biologically inert compounds
Lipolysis: breakdown of lipoproteins
Antithrombogenic: platelets can not reach the subendothelial collagen

Front 8

1.What are the Weibel-Palade granules?

Back 8

Elongated, multitubular structures (1 to 2.5 µm by 0.1 µm), characteristic of endothelial cells. They are storages of von Willebrand factor, interleukin 8, endothelin and P-selectin.

Front 9

1.What are the pericytes?

Back 9

Mesenchymal-like cells, make the media of the capillaries and can modify their diameter. They have a big potential to differentiate into other cells.

Front 10

1.What types of capillary vessels exist?

Back 10

Continuous or somatic: Most closed, cells with intact cytoplasm.
Fenestrated: The cell cytoplasm has holes (fenestrae) with diaphragms
Fenestrated without diaphragms: The fenestrae are constantly opened.
Sinusoidal: Fenestrae plus gaps between the cells. Most open.

Front 11

1.What are the capillary sphincters?

Back 11

Capillaries are unable to resist even minor increases on hydrostatic pressure, so “something” is needed to lower the blood pressure before it enters the capillary bed, and that “something” is the arteriolar muscle and also the capillary sphincters

Front 12

1.Describe the arterioles.

Back 12

Very thin subendothelial layer and adventitia
Only the bigger ones have internal elastic lamina
Media: Circular layers of smooth muscle (appearance of strength)

Front 13

1.Describe the small arteries.

Back 13

Resistance vessels that slow the blood flow to prevent the rupture of capillary vessels. They have up to ten layers of smooth muscle in the media.

The contraction of these vessels raises the arterial blood pressure.

Front 14

1.Describe the muscular arteries.

Back 14

Most of the named ones;they are also called distributing arteries
Intima: Thick subendothelial layer with scant smooth muscle
Internal elastic lamina prominent
Media: Muscular, with 25 – 40 layers of smooth muscle, elastic and reticular fibres (plus proteoglycans)
Adventitia: Well developed

Front 15

1.Describe the elastic arteries.

Back 15

Aorta and its larger branches; pulmonary artery. They are yellowish due to their elastin content
Intima: Thicker / subendothelial layer thick
Internal elastic lamina not very evident (hidden by the other laminae)
Media: 40 – 70 concentrically arranged perforated elastic laminae, apparent absence of external elastic laminae

Front 16

1.What are the carotid bodies and what stimuli they detect?

Back 16

Chemoreceptors near the bifurcation of the common carotid artery.
Detect increases of CO2 and decreases of O2 and of the pH (acidosis), increasing the respiratory rate as result.

Front 17

1.What types of cells make the carotid bodies?

Back 17

Glomus cells (type I) and sheath cells (type II)

Front 18

1.What other bodies have similar chemoreceptive functions?

Back 18

Aortic bodies and the jugular glomera: Similar functions.

Front 19

1.What are the carotid sinuses and what stimuli they detect?

Back 19

At the wall of the internal carotid artery
Baroreceptors
Stimulation produces a drop in arterial pressure.

Front 20

1.Describe the venules.

Back 20

Intima: Endothelium
Media: Thin, with few muscle cells
Adventitia: Prominent, blends with the surrounding connective tissue

Front 21

1.Describe the small and medium veins.

Back 21

Intima: it creates valves (semilunar folds of the intima projected into the lumen); thin or absent subendothelial layer.
Media: small bundles of smooth muscle
Adventitia: well developed

Front 22

1.Describe the large veins.

Back 22

Intima: well developed, very well developed valves.
Media: thinner, few layers of smooth muscle cells
Adventitia: thickest and best developed, with cardiac muscle near the end of venae cavae and pulmonary vein, or smooth muscle in large veins below heart level
Adventitial muscle provides strength to the vein.
Circular plus longitudinal bundles of smooth muscle cells provide with antigravity peristaltic movements.

Front 23

1.What are the two functions of the heart?

Back 23

Mechanical function: pumps blood to other organs and itself
Hormonal function: secretion of atrial natriuretic factor

Front 24

1.What is the endocardium?

Back 24

Equivalent to the intima in blood vessels
Endothelial cells over a subendothelial layer.

Front 25

1.What is the myocardium?

Back 25

Equivalent to the media of blood vessels
Cardiac muscle cells (17 – 25 µm in diameter / 60 – 140 µm in length) in spiral layers. These cells include:
Contractile cells.
Impulse generator cells (at the nodes)
Conductive cells (connect the nodes with the contractile cells).

Front 26

1.What is the epicardium?

Back 26

Also known as visceral pericardium, it is the equivalent to the adventitia of blood vessels.
Serous covering of the heart, with mesothelium (simple squamous epithelium) and a thin layer of connective tissue.
In some areas it has big amounts of adipose tissue.

Front 27

1.What is the hierarchy in the control of the heartbeat?

Back 27

Sinoatrial node > Atrioventricular node > Purkinje fibres

Front 28

1.What is the sinoatrial node and how can it be identified?

Back 28

Pacemaker of the heart. It is an irregular meshwork of muscle fibres 3-4 µm in diameter, without striation pattern or intercalated disks (cells attached with just desmosomes), few myofibrils, the cells are embedded in connective tissue. There are numerous blood vessels and a prominent, central and constant structure, the nodal artery. There are nerve fibres at the periphery of the node

Front 29

1.What is the atrioventricular node and how can it be identified?

Back 29

Receives the impulse of the sinoatrial node through the anterior, posterior and middle internodal tracts (indistinguishable from the other atrial fibres).
Made of muscle fibres identical to those of the sinoatrial node, although less haphazardly arranged, intertwined with connective tissue, vessels and nerves

Front 30

1.What is the Bundle of His?

Back 30

The bundle of His is made of fibres of the anterior end of the atrioventricular (AV) node which are more regularly arranged and become a bundle of parallel fibres divided in right and left branches without particular morphologic features.

Front 31

1.Describe the Purkinje fibres.

Back 31

Large modified cardiac fibres with abundant and vacuolated sarcoplasm (rich in glycogen), scant and peripheral myofibrils

Front 32

1.Characterize the large lymphatic vessels.

Back 32

Similar to a vein but with more muscle in the media. The adventitia is poorly developed, with vasa vasorum and nerves