Biology: The Heart

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Heart Visit Nova: The Heart


1. Ischemia- Lethargy of cells due to the shortage of oxygen.

2. Angina- or chest pain, due to the high oxygen demand of the heart muscles and lack of adequate oxygenation by the coronary arteries. Angina can be caused by, atherosclerosis, hypertension, stress, thyroid diseases and others.

3. Myocardial Infarction- Commonly called "heart attack" Death of myocardium due to inadequate oxygenation. In MI the dead cardiac tissue is replaced by noncontractile scar tissue that ultimately leads to reduction in heart muscle strength. Note: MI is usually due to the rupture or blockage of one of the coronary arteries....

Diffusion In Capillaries Occurs As Follows:

A. Small molecules and ions like water and glucose and K+ diffuse through specific pores of the capillary endothelial cell membrane.

B. Lipid-soluble substances like steroids, pass through the plasma membrane without difficulty.

C. Gases diffuse freely through any part of the capillary plasma membrane.

D. Large nonsoluble proteins-ex. glycoproteins-are transported from one side of the capillary cell wall via pinocytosis and expelled on to the other side of the capillaries.

Human Circulatory System:

Map of the Human Heart

Video: How Does the Heart Work?

I. Heart:
1. Systematic Circulation- This is the pathway where 
the oxygen rich blood is pumped throughout the body 
as it starts from the left ventricle and atrium going 
to the body and back to the right atrium and ventricles. 

2. Pulmonary Circulation- This is a process whereby the 
deoxygenated blood from the body is pumped into the lungs
where it is oxygenated. The oxygenated blood then moves 
back to the left atrium and left ventricle of the 
heart to be pumped to the body. 

Note: Fish have a single chamber heart; amphibians 
have a two chambered heart and 
mammals and birds have a four chambered heart. 

II. The Whole Blood Circulation Is As Follows: 

1. Oxygenated blood enters the left atrium from the left 
and right pulmonary veins (body's only oxygen rich veins). 

2. The left atrium contracts and pushes all of the 
blood through the bicuspid valve into the left ventricle. 

3. The left ventricle's contraction is to push the blood 
out of the left ventricle via aorta and its several 
arterial branches into the body. 

4. When the deoxygenated blood from other tissues of 
the body reaches the right atrium, the right atrium 
pumps blood out into the right ventricle through the 
tricuspid valve. 

5. When the right ventricle is filled with blood 
it will contract and pump all of its content into 
the lungs hrough the pulmonary valve. Hence, the 
pulmonary artery is the body's only artery with
deoxygenated blood. ... 

Structure and Function of Blood

Guide to Blood Groups

IV. Electrocardiogram- Atrial Systole- (atrial contraction) -When the SA-node is excited and the atrium contracts about 1/3 of the atrial blood enters the ventricles. The other 2/3 of the blood enters the ventricles during the diastolic phase. This cycle is as follows: 1. 1/3 of blood has left the atrium and is in the ventricles. 2. The impulses from the S-A node have reached the A-V node through the Purkinje fibers, resulting in the contraction of ventricles. 3. Ventricle contraction closes the bicuspid and tricuspid valves of the atrioventricular valves and opens the pulmonary and aortic semilunar valves. This allows the blood to flow out of the ventricle. This phase is also called the systolic phase of the ventricles. 4. The diastolic phase (or relaxation phase) of the ventricle occurs when the ventricle has no blood, the pulmonary and aortic semilunar valves are shut and the inside pressure of the ventricles tend to become lower than the atrial pressure. 5. Due to low ventricular pressure, the bicuspid and tricuspid valves open and release their blood into the ventricles. This is when the rest of the 2/3 of the blood in the atria enters the ventricles. ELECTROCARDIOGRAM (EKG) EKG is the recording of electrical currents that occur in the cyclic functioning of the heart. The segments of the deflection curve are as follows: P-Wave- Atrial depolarization or dispersal of impulses from SA-node to the AV-node. SA-node depolarization leads to atrial contraction. QRS Wave- Ventricular excitation due to the spreading of electrical impulse along the ventricles. T-Wave-Ventricular relaxation. Note: There is no pick representing the atrial relaxation because it is hidden within the large ventricular depolarization pick. V. Characteristic Of The Heart Beat- The heart beat has a lub- dab, lub-dub sequence of beatings. The lub and dab sound is due to the closure of the bi-and tricuspid valves and lub and the dub sound is due to the closure of the pulmonary and aortic semilunar valves, respectively. When a hissing or sloshing sound is heard with the stethoscope then there is a malfunction of the heart valves. These problems are due to incomplete closure of any of these two sets of valves and the condition is commonly called "Heart Murmur." This disease can be caused by infections like rheumatic fever and or congenital malformations like abnormal formation of valves in the newborn. VI. Strenuous Physical Activities- Results an increases in: skeletal muscle blood flow, systolic arterial pressure, heart rate, arterial pressure, stroke volume and cardiac output, while blood flow to the visceral organs, like the kidneys and intestines, is reduced. VII. Heart Rate Control- The nervous system control of the heart rate is within the medulla oblongata of the brainstem. There are two kinds of nerves: 1. Parasympathetic- Which are within the vagus nerve (cranial nerve X) and function to decrease the heart rate. 2. Sympathetic- This is controlled by the nerve fibers that also come from the medulla oblongata, and like the parasympathetic nervous system they stimulate the SA-node. Sympathetic nerve impulses tend to increase the heart rate when triggered. 3. Inhibitory Substances- These are compounds that when present tend to prevent cardiac contractions. Acetylcholine is an example of annhibitory neurotransmitter on the cardiac system. 4. Excitatory Hormones- These are hormones that will increase the heart rate. The most common of these hormones is epinephrine. This hormone is secreted by the adrenal medulla during stress and fright and triggers the fight-or-flight response. Recalling that other effects of epinephrine are vasoconstriction in visceral organs and smooth muscles and increased blood flow and vasodilatation in skeletal and cardiac muscle. Hence, epinephrine results in an increase of blood pressure. ... HYPERTENSION- Or high blood pressure, a disease that affects the heart and blood vessels. The sign of hypertension is a blood pressure reading of 140/90 (systolic/distolic). There are many factors which contribute to hypertension development. However, the most important ones are hormonal, and Fatty deposits within blood vessels. 1. Hormonal- This is a case where the adrenal cortex secretion of aldosterone increases. Aldosterone stimulates the kidney tubules to reabsorb more Na+. This results in the simultaneous retention of H2O. As the amount blood water increases, so does blood volume, resulting in increasing stroke volume and consequent increase in cardiac output, and ultimately increase of arterial blood pressure. This can be prevented by reduction of Na+, salt consumption. Damage to the kidney may result in over secretion of the hormone renin. Renin functions as the enzyme that converts liver synthesized glycoprotein angiotensinogen conversion into angiotensin. Angiotensin II can both constrict and stimulate kidney aldosterone secretion. Any of the above conditions will result in increased blood pressure and hypertension. 2. Fatty acids- Deposited on the surface of the arteries and veins may create a barrier that restricts the passage of blood. This causes resistance that might ultimately lead to higher heartoutput, increased blood pressure and finally hype