Cardiovascular system overview Presented 2011 / 2012 by: Dr Magdi El Sersi Assistant Prof of Medical Physiology Basic Medical Sciences Department Ext. 7243 E mail: email@example.com
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MAIN FUNCTIONS OF THE CIRCULATORY SYSTEM• Transport and distribute essential substances to the tissues.• Remove metabolic byproducts.• Adjustment of oxygen and nutrient supply in different physiologic states.• Regulation of body temperature.
The system has two majordivisions:v A pulmonary circuit :which carried blood to thelungs for gas exchange andreturns it to the heart.v A systemic circuit :which supplies blood toevery organ of the body.
The rightside of theheart servesthe The left sidepulmonary serves thecircuit systemic circuit.
The heart is enclosed in a double-walled sac called the pericardium. The outer wall, called the parietal pericardium (pericardial sac). has a tough, superficial fibrous layer of dense irregular connective tissue and a deep, thin serous layer. The serous layer turns inward at the base of theheart and forms the visceral pericardium (epicardium)covering the heart surface .
The pericardium The pericardial sac is anchored by ligaments to thediaphragm below and the sternum anterior to it. Between the parietal and visceral membranes is a space called the pericardial cavity . It contains 5 to 30 mL of pericardial fluid.
The pericardial fluid Pathophysiology : Pericardiallubricates the membranes disease manifest itself by theand allows the heart to accumulation of fluid in thebeat almost without pericardial space (pericardialfriction. effusion) and /or inflammation of the pericardium (pericarditis). The pericardial cavity can fill with up to 2 litters of serous fluid (hydropericardium ) or blood (hemopericardium) that prevent normal diastolic filling and thereby reduces cardiac output.
COLLECTING PUMP TUBULES THE MAIN CIRCUITDISTRIBUTING THINTUBULES VESSELS
There are 3 primary blood vessel types:1. Arteries : which carry blood away from the heart.2. Veins : which carry blood towards the heart.3. Capillaries : tiny blood vessels that function in the exchange of gases, nutrients, and wastes between the blood and the interstitial fluid.
The walls of both arteries and veins have 3 layers that surround the lumen:1. Tunica externa Outermost layer. Made primarily of loose connective tissue. Anchors the blood vessel to the surrounding tissue.2. Tunica Media Consists primarily of smooth muscle and is responsible for vasoconstriction and vasodilatation. Usually the thickest layer in arteries.3. Tunica Interna (Endothelium) Acts as a selectively permeable barrier to blood solutes.Secretes vasoconstrictors and vasodilators.Provides a smooth surface that repels blood cells and platelets.
They are constructed to withstandsurges of blood pressure associated withventricular systole.•Theyre more muscular than veins and appearrelatively round in tissue sections.• They retain their round shape even when empty. There are 3 basic categories of arteries
1. Conducting (or Elastic) ArteriesThe largestExamples include the aorta, pulmonary arteries,and the common carotid arteries.
Their tunica media contains agreat deal of elastic tissue.The elastic tissue allows forexpansion during ventricularsystole and recoil duringventricular diastole.This helps create continuousflow from a discontinuouspump.
Conducting arteries expand during ventricular systole toreceive blood, and recoil during diastole: *Their expansion takes some of the pressure off the blood so thatsmaller arteries downstream are subjected to less systolic stress .•* Their recoil between heart beats prevents t he bloodpressure from dropping too low while the heart is relaxingand refilling. Lessen the fluctuations in blood pressure
2. Distributing (or Muscular) Arteries Smaller branches ,distribute blood to individual organs.They have 25-40 layers of smooth muscle cellsconstituting about three quarters of the wall thickness.Examples include the brachial, femoral, and splenic arteries
3. Arterioles •Smallest of the three. • They are heavily innervated . • The primary points at which the body controls the relative amounts of blood directed to specific organs.
Linking the arterioles to the capillaries are short vessels known as metarterioles. Part of their wall surrounded by smooth muscleThese muscle cells form precapillary sphincters whichencircle the entrance to a capillary bed.
These sphincters regulate how much blood will flowthrough particular capillary beds.
Arterial sense organs:Certain major arteries abovethe heart have sensorystructures in their walls thatmonitor blood pressure andchemistry.They transmit information tothe brain stem that is used toregulate the heart beat,vasomotion and respiration.
The sensory receptors are of three kinds 1. Carotid sinuses. These are baroreceptors (pressure sensors) that respond to changes in blood pressure. * Thin tunica media * An abundance of glossopharyngeal nerve fibers in the tunica externa. A rise in blood pressure stretches the thin media and stimulates the nerve fibers which transmits signals to theThe carotid sinuses vasomotor and cardiac centers of theare located in the brainstem, which responds by loweringwall of the internal the heart rate and dilating the bloodcarotid artery vessels, thereby lowering the blood pressure.
2. Carotid bodies: located near the branch of the common carotid arteries. They are chemoreceptors that monitor changes in blood composition. They primarily transmit signals to the brainstem respiratory centers, which adjust breathing to stabilize the blood pH and its CO2 and O2 levels
3. Aortic bodies: These are oneto three chemoreceptorslocated in the aortic archThey are structurally similar to the carotid bodies and havethe same function.
Capillaries There are approximately 1 billion of them in the human body.Capillaries are organized into groups of 10-100 in capillary beds There are 3 separate types of capillaries: 1. Continuous Capillaries 2. Fenestrated Capillaries 3. Sinusoidal Capillaries
1. Continuous Capillaries Most common. Abundant in skin and muscle. Endothelial cells are joined by tight junctions. but contain intercellular clefts through which small molecules (e.g., glucose, but not albumin) can pass.Cerebral capillaries lack these clefts and have far morenumerous tight junctions forming the blood brain barrier whichhelps protect the delicate brain tissue from blood-borne toxinsand pathogens.
Some continues capillariesexhibit cells called pericytesthat lie external to theendothelium Pericytes are contractile, have elongated tendrils that wrap around the capillary It thought that they contract and regulate blood flowthrough the capillaries.They also can differentiate into endothelial and smoothmuscle cells and thus contribute to vessel growth andrepair.
2. Fenestrated capillaries These pores allow for the rapid passage of molecules, even proteins , through the capillary wall. Found in sites of activeSimilar to absorption (small intestine),continuous secretion (endocrinecapillaries but organs) and capillarysome of the filtration (kidneys).endothelial cellshas filtration poresfenestrations.
3. Sinusoidal Capillaries Highly modified, extremely leaky, fenestrated capillariesContain irregularly shaped lumen and large intercellular clefts Found in sites where large stuff needs to exit/enter the bloodstream. Such sites include bone marrow (for passage of nascent blood cells), lymphoid organs (for easy entry/exit by WBCs) and the liver (for large plasma proteins, e.g., albumin).
In the liver and the spleen , theendothelium is intimatelyassociated with macrophages.In these locations the sinusoidsare twisty and tortuous,conformed to the shape of thesurrounding tissue. . Thetwistiness makes blood flowextra slowly which gives timefor splenic and hepaticmacrophages to monitor andassess its contents.
Just by looking at this image, can you identify thedifferent capillary types?
Veins The capacitance vessels of the cardiovascular system because : They are relatively thin-walled and flaccid. Expand easily to accommodate an increased volume of blood.At rest, about 54% ofthe blood is found inthe systemic veins ascompared with only11% in the systemicarteries
Being distant from the ventricles of the heart,they are subjected to relatively low bloodpressure.In large arteries, blood pressure averages 90 to100 mm Hg (millimeters of mercury) andsurges to 120 mm Hg during systole, whereasin veins it averages about 10 mm Hg.Considering the relatively low pressure inthe veins. how blood is forced through them to get back to the heart????
Its a combination of 3 separate things:1.Skeletal Muscle Pump .2. Respiratory Pump .3. Venous Valves
Its a combination of 3 separate things: 1.Skeletal Muscle Pump . 2. Respiratory Pump . 3. Venous Valves1. Skeletal Muscle Pump :- the contraction/relaxation cycles of skeletal muscles squeeze the veins forcing the contained blood towards the heart.
2. Respiratory Pump : as we inhale, our thoracic cavity expands while our abdominal cavity compresses. pressure within veins of the thoracic cavity drops. Meanwhile, pressure in the abdominal veins increases. This combination results in increased blood flow towards that heart.
3. Venous Valves: - one-way valves (similar to the semilunars of the heart) made of flaps of endothelium are found in medium veins (mostly in the legs and the arms) where they help prevent backflow.
Pathophysiology: varicoseveins:In people who stand for longperiods, blood tends to pool in thelower limbs and stretch the veins.This is especially true of superficialveins, which are not surrounded bysupportive tissue.Stretching pulls the cusps of thevenous valves farther apart until thevalves become incompetent toprevent the backflow of blood
As the veins become furtherdistended, their walls growweak and they develop intovaricose veins with irregulardilations and twisted pathways.