Visit Nova:The Heart DISEASES OF 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:

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. ... 


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