Lecture 18- Circulatory system Flashcards
What does a circulatory system consist of?
A muscular pump (heart)
A fluid (blood)
A series of conduits (blood vessels)
What is the heart, blood and blood vessels known collectively as?
Cardiovascular system
What is the function of circulatory systems?
To transport things around the body- heat, hormones, respiratory gases, blood cells, platelets, immune system, nutrients, waste products
What organisms do not have circulatory systems?
Single celled organisms, multicellular organisms with cells close to the external environment
Why do some animals not need circulatory systems?
Exchange can occur directly with the external environment due to structures and body shapes (such as gastrovascular cavities)
What are gastrovascular cavities?
Highly branched central cavities
In larger animals, what environment do cells exchange with?
The extracellular fluid
What does the extracellular fluid consist of?
Fluid in the circulatory system (blood plasma)
Fluid around the cells (interstital fluid)
What is an open circulatory system?
Where extracellular fluid combines with fluid of the circulatory system and squeezes through intercellular spaces when the animal moves.
How does fluid return to the heart in an open circulatory system?
In arthropods- through ostia
In mollusks- open vessels
What is a closed circulatory system?
Where blood is kept separate from the interstital fluid
How does blood move through a closed circulatory system?
Blood is pumped through the vascular system by one or more hearts
What are the three main advantages of a closed circulatory system?
- Faster transport through vessels than intercellular spaces
- Blood directed to specific tissues
- Specialized carriers travel in vessels and transport hormones or nutrients to specific sites
What does the right side of the heart do?
Pumps blood through the pulmonary circuit
What does the left heart do?
Pumps blood through the systemic circuit
What are the two types of chambers?
Atria, ventricles
What is the purpose of valves in the heart?
To prevent backflow of blood
What valve lies between the atria and ventricles?
Atrioventricular valves
What do atrioventricular valves do?
Prevent backflow when ventricles contract
What valves lie between the ventricles and major arteries?
The pulmonary valve
The aortic valve
What is the purpose of the pulmonary valve and the aortic valve?
Prevent backflow when ventricles relax
What are the three steps of blood flow through the right side of the heart?
Deoxygenated blood from tissues enters the right atrium
Flows through atrioventricular valve into right ventricle
Right ventricle pumps blood through pulmonary valve into pulmonary circuit
What veins does the right atrium receive blood from?
- Superior vena cava (from upper body)
- Inferior vena cava (from lower body)
What veins does oxygenated blood return to the heart in?
Pulmonary veins
What are the two phases of of the cardiac cycle?
Systole
Diastole
What is systole?
When ventricles contract
What is diastole?
When ventricles relax
What is the 1st step in the cardiac cycle?
The atria contract
What is the next step after the atria contract?
'lub' Ventricles contract AV valves close Pressure in ventricle builds Pulmonary/aortic valve opens
What happens after the ‘lub’ stage?
Blood is pumped out of the ventricles, into the aorta and pulmonary artery.
What happens after blood is pumped out of the ventricles into the aorta and pulmonary arteries?
‘Dup’
Ventricles relax
Pressure in ventricle falls at the end of sytole
Aortic/pulmonary arteries shut
The the ventricles fill with blood again
How are blood pressure changes measured?
Sphygmomanometer and a stethoscope
What is the systolic value?
The pressure needed to compress an artery so blood does not flow
What is diastolic value?
Pressure needed to allow intermittent flow through the artery
What are healthy blood pressure values?
120 mm Hg over 70 mm Hg
What is blood?
A connective tissue made of cells in a liquid extracellular matrix called plasma
What is the name of the part of the blood made up of cells?
Packed cell volume or hematocrit
What are most of the cells in the hematocrit?
Erythrocytes- red blood cells- that transport gases
Where are red blood cells generated?
Bone marrow
What is hypoxia?
Deficiency in the amount of oxygen reaching tissues
What is produced in response to hypoxia?
Erythropoietin- a hormone released by the kidneys
What activates the genes for erythropoietin in the kidneys?
Hypoxia-inducible factor 1 (HIF-1) a transcription factor
How are red blood cells formed?
Immature red blood cells divide and produce hemoglobin while in the bone marrow,
At 30% hemoglobin the organelles break down
The cell enters circulation
How long do red blood cells circulate?
About 120 days
What happens to red blood cells after 120 days?
They rupture as the pass through narrow capillaries, as in the spleen
Other than red blood cells, what else does bone marrow produce?
Megakaryocytes
What do megakaryocytes do?
Break off cell fragments called platelets
What do platelets do?
Initiate blood clotting when activated by collagen exposed in damaged blood vessels
What do platelets do once activated?
Release chemical clotting factors which activate other platelets
What are the 4 main steps in blood clotting?
- Cell damage and platelet activation
- Inactive enzyme prothrombin converts to active form, thrombin
- Thrombin cleaves fibrinogen and forms fibrin
- Fibrin threads form mesh that clots blood and seals vessels
Where is prothrombin and fibrinogen found?
Circulating in the plasma
What does plasma contain?
Gases Ions Nutrients Proteins Other molecule: hormones, vitamins
What type of vessel are arteries and arterioles?
Resistance vessels because their resistance can vary
How does the resistance of arteries and arterioles vary?
- Walls have elastin and collagen- stretch and recoil
- Smooth muscle cells in the walls allow them to dilate/constrict.
What other feature of a resistance vessel can change its resistance?
Its diameter
How is the resistance of an artery or arteriole controlled?
By neuronal and hormonal mechanisms by influencing smooth muscle cells
Why is pressure reduced in smaller vessels such as capillaries?
- Arterioles are highly branched
- Capillaries contribute an enormous surface area
What is the structure of a capillary?
Walls are a single layer of endothelial cells, tiny holes called fenestrations
What are capillary beds permeable to?
Water, ions, small molecules
Not large proteins
What are Starling’s forces?
Two opposing forces that maintain water balance in capillaries
How do starling’s forces work?
- Blood pressure: forces water and small solutes out
- (Colloidal) Osmotic pressure: created by large molecules that cannot leave
Explain how blood pressure changes across a capillary bed.
Blood pressure is higher at the arterial end and drops at the venous end
How does osmotic pressure change across a capillary?
It does not change- it is constant
How does blood pressure and osmotic pressure work together in a capillary?
Blood pressure is higher than osmotic pressure: fluid leaves
Blood pressure is lower than osmotic pressure: fluid returns
What is Edema?
An accumulation of fluid in the extracellular space.
What can cause edema?
- Fall in blood protein levels (disease)
- Histamine release: increases capillary permeability, relaxes smooth muscle in arterioles, raises blood pressure in capillaries
Other than changes in blood pressure, what else draws water back into capillaries?
Bicarbonate ions (HCO3-) converted from CO2 contribute to the osmotic pressure- more at the venous end raises osmotic pressure.
What is the blood-brain barrier?
Highly selective brain capillaries which do not have fenestrations
What are veins also known as?
Capacitance vessels
Why are veins called capacitance vessels?
Because they are very expandable so blood will accumulate in them
How is blood returning from below the heart assisted?
Skeletal muscle contractions that squeeze the veins
How is backflow prevented in veins?
One-way valves
What is the Frank-Starling law?
A property of cardiac muscle cells that increases cardiac output
What are the implications of the Frank-Starling law?
Cells contract more forcefully if stretched by an increase in the volume of returning blood
What does the lymphatic system do?
Returns interstital fluid to the blood
What is it called when fluid enters the vessels?
lymph
Where do lymphatic capillaries go?
Merge into thoracic ducts- they empty into veins in the neck
What are lymph nodes?
Sites of lymphocyte production
What do lymph nodes do?
Remove microorganisms and foreign material by phagocytosis and act as filters.
What is atherosclerosis?
Hardening of the arteries
How does atherosclerosis form?
-Endothelial lining is damaged by high blood pressure, smoking, diet, microorganisms
Plaque forms at site of damage
Damaged cells attract migration of smooth muscle cells
What happens once smooth muscle cells have been attracted to damaged cells?
Smooth muscle cells have cholesterol deposits to make the plaque fatty
Connective tissue and calcium deposits make the artery wall less elastic
What can happen if platelets stick to plaque on artery walls?
A thrombus may form
What do coronary arteries do?
Supply blood to the heart muscle
What are the symptoms of atherosclerosis?
Chest pain, shortness of breath (reduced blood flow in coronary arteries)
What happens if a thrombus forms in the coronary artery?
Coronary thrombus: myocardial infarction (heart attack)
What is an embolus?
A piece of thrombus
what can an embolus cause?
Embolism if it lodges in a blood vessel
What happens if the embolism is in the brain?
Cells fed by that artery die: a stroke
What are some of the causes of atherosclerosis?
- Genetic predisposition
- Age
- Environmental risk (smoking, high-fat diet, sedentary)
- Medical conditions (hypertension, obesity, diabetes)
