Capillary fluid exchange

Two factors determine the movement of materials in and out of capillaries: blood pressure and osmotic pressure

Because BP decreases as blood travels further from left side of the heart, the BP on the arteriolar and of the capillary is greater than at the venule end

Osmotic pressure (OP) results primarily from the presence of plasma proteins and minerals (salts)

OP stays relatively constant Blood plasma (fluid) contains dissolved solutes

that are small (minerals, aa's, glucose, etc) At capillary end, BP>OP, therefore, fluid with

dissolved solutes moves into tissues In the middle, BP = OP therefore, nutrients and

wastes move based on concentration gradients At venule end, BP<OP, therefore fluid and

solutes are drawn into capillary

RBC and plasma proteins too big to pass out of capillaries

Circulatory diseases

Hypertension High blood pressure caused by

increased resistance to blood flow High BP puts extra strain on heart, so

heart must work harder to move blood

Causes of hypertension Stress: causes stimulation of sympathetic

nervous system, which leads to constriction of arteries (vasoconstriction). This causes kidneys to secrete renin, a hormone that brings high BP due to sodium retention (increase blood volume)

Diet: high in salt causes water retention (increased blood volume and BP)

Athersclerosis: build up of plaque in arteries decreases capacity of artery, increases BP

Hypotension

Decreased BP resulting in decreased blood flow to the brain and heart. Body responds by stimulating nervous system (stress reaction)

Causes: Blood loss extreme emotion (leads to fainting) genetic

Athersclerosis vs Arteriosclerosis

Arteriosclerosis means hardening of arteries Arteries become rigid, may decrease in

diameter and lose elasticity Atherosclerosis is a type of this in which plaque

build up is the cause Can lead to strokes and heart attacks

Stroke and heart attack

A stroke occurs when brain tissue dies as a result of lack of blood flow

Can be result of an embolism blocking the blood flow (piece of plaque) in the brain

A heart attack occurs when heart muscle tissue dies as a result of a lack of blood flow

Caused by a blockage of coronary arteries Early stages of heart attack results in angina

(chest pains)

Aneurysm

Weakened artery wall Can rupture resulting in hemorrage Results in lack of blood – oxygen to particular

tissues

Varicose veins

Valves in veins become weak and lose function Decrease of blood flow therefore increased

volume stays in the veins

The autonomic nervous system directs all activities of the body that occur without a person's conscious control

It has two parts: the sympathetic division, which is most active in times of stress, and the parasympathetic division, which controls maintenance activities and helps conserve the body's energy.

Sympathetic and parasympathetic nervous system