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Human BiologyLecture 1: Functional histology: heart and blood vessels
Two cardiovascular pathways:
1. Pulmonary circuit: circulates blood through the lungs
• Right atrium pumps deoxygenated blood into the right ventricle, which
pumps it into the pulmonary trunk
• The pulmonary trunk splits into right and left pulmonary arteries which go to
the lungs
• In the lungs, the pulmonary arteries branch into arterioles which lead to
capillaries. This is where gas exchange occurs
• The pulmonary capillaries lead to venules which merge into the pulmonary
veins
• The four pulmonary veins empty into the left atrium
2. Systemic circuit: circulates blood through the body tissues
Chordae tendineae: they connect the valve with papillary muscles
Blood flow through the heart:
• The superior vena cava and inferior vena cava carry O2-poor, CO2-rich blood from
the body to the right atrium
• Blood then flows through the right AV (tricuspid) valve into the right ventricle
• The right ventricle pumps blood through the pulmonary valve into the pulmonary
trunk, which branches into right and left pulmonary arteries → they lead to arteries
• The pulmonary veins carry O2-rich, CO2-poor blood from the lungs to the left atrium
• Blood then flows through the left AV (bicuspid) valve into the left ventricle
• The left ventricle pumps blood through the aortic valve into the aorta
The SA node (pacemaker) in the right atrium initiates the heartbeat by sending out an
electrical signal → the atria contract. The AV node sends a signal down the AV bundle
(longitudinal cells) and Purkinje fibers to all parts in the wall of the heart. Ventricular
contraction occurs via the Purkinje fibers.
Extrinsic control: the cardiac control center in the brain increases or decreases the heart rate
depending on the body’s needs.
,Figure 1: The heart
ECG: electrocardiogram recording
Figure 2: ECG
• Endocardium: one layer of flat epithelium → endothelium and a little bit of
connective tissue
• Myocardium: totality of all heart muscle cells:
, • Epicardium/Pericardium: surrounding the heart (big blood coronary vessels are
located)
The heart muscles cells need oxygen and glucose continuously, and the heart works non-
stop: that’s why capillaries are needed.
Intercalated disc: dark lines in microscopy: consists of cell-cell connections. Consists of fascia
adherens, desmosomes and nexus connections
Purkinje fibers: less actin and myosin
Blood vessels:
2 types of arteries: all of them except from one, the aorta (elastic artery: extra elastin) are
muscular arteries.
Muscular artery:
• tunica intima (internal layer),
endothelium with basal lamina,
subendothelial layer (connective tissue),
lamina elastica interna[zig zag] (elastic
fibers, black line of the lumen), veins do
not have it
• tunica media, smooth muscle cells
(circular), also elastic and collagen
fibers, sometimes lamina elastica
externa (firs layer of the border between
media and external layer)
• external layer, mainly connective tissue,
smooth muscle cell, collagen fibers,
elastin fibers. cells there need oxygen
and nutrients (because they are far away
from the lumen) so there are small
blood vessels supplying them → vasa
vasorum (stained black)
The aorta has lots of elastic fibers in the media
besides smooth muscle cells → large flexibility
and relatively constant pressure gradient
Figure 3: elastic artery
A muscular vein has a larger lumen, smaller
media, wider external layer and does NOT contain the lamina elastica interna.
- Artery: 1-13 mm (~1cm)
- Arteriole: 30-300 μm
- Capillary: 10 μm
- Venule: 30-300 μm
, - Vene: 0.1-10 mm
Arterioles:
- Small diameter
- Endothelium
- Lamina elastica interna
- 1-3 smooth muscle cells (its media)
Venule:
- Small diameter
- Endothelium
- NO lamina elastica interna
- 1-3 smooth muscle cells (its media)
Capillary:
- Very small diameter Figure 4: Muscular artery and muscular vein
- Endothelium
- NO lamina elastica interna
- NO smooth muscle cells
- They uptake nutrients and O2 and remove waste and CO2
- 3 types:
1. Continuous: with basal lamina, the most common type
2. Fenestrated: with basal lamina and small holes (fenestrae) (hormone producing
cells and kidney)
3. Sinusoid capillary: with discontinuous basal lamina, with large pores (liver,
spleen and bone marrow)
Arteriole-venule anastomosis (AA) → in the skin sometimes the blood does not go to the
capillary network but through the AA to the venules (a shortcut) directly from an artery. If it
goes to the capillaries then we have for example blushing.
Oxygen levels are high in the lung capillaries and the arteries. In the capillaries and the veins,
it’s low.
Large veins have valves that are the extensions of the intima, helps the blood to travel back
up from the extremities.
Lecture 2: Hemopoiesis-red blood cells
Hemopoiesis is the new formation of blood cells.
Composition of whole blood
Centrifugation of peripheral blood will lead to erythrocytes in the bottom, plasma (water,
proteins, other solutes) on top and buffy coat (containing neutrophils) in the middle.
Plasma: extracellular material, cell-free part of the blood treated with anti-coagulants.
Serum: pale yellow liquid, contains growthy factors and other proteins released from
platelets during clot formation.
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