Biomedical Science - Blood pressure & lymphatic system

Tunica intima

smooth layer of squamous epithelial cells (endothelium) on a base of collagen

Tunica media

smooth muscle, allows contraction to increase blood pressure

Tunica externa

protects outside of vessel

capillaries only have

tunica intima

arteries and arterioles

Carry blood AWAY from the heart to organs, walls are thick to withstand high blood pressure from heart

Arteries - 2 types

large/elastic or medium/small/muscular

Arterioles (tiny)

30 microm, deliver blood to capillaries, lower pressure

veins and venules

Carry low pressure blood back to the heart, less smooth muscle and elastin than arteries, contains valves, to ensure 1 way blood flow to heart venules are tiny veins with no valves

capillaries

single layer of endothelial cells, thin basement membrane, transport blood throughout tissues (perfuse the tissues) with oxygen and nutrients, thin wall enables diffusion of substances across capillary wall, diameter is same as a RBC 7-8 micrometres

blood pressure definition

pressure that blood exerts on the wall of the blood vessels

SYSTOLIC blood pressure

max pressure within the large arteries when the heart muscle contracts

DIASTOLIC blood pressure

lowest pressure within the large arteries during heart muscle relaxation

Blood pressure in arteries is affected by

Cardiac Output and Peripheral Vascular Resistance

if either CO or PVR increase BP will

also increase

CO

the volume of blood pumped by the heart in 1 minute, depends on HR and Stroke Volume (amount of blood ejected from LV in 1 contraction)

formula for CO

HR x SV

CO is a measure of

how effectively the cardiovascular system is working

Peripheral vascular resistance

the resistance to blood flow in the arterioles

High resistance occurs during

vasoconstriction

High resistance in vasoconstriction

sympathetic stimulation causes constriction, diameter of vessel decreases, PVR increases, higher blood pressure results

Low resistance in vasodilation

reduction in sympathetic stimulation causes dilation, diameter of vessel increases, PVR decreases, lower blood pressure results

Baroreceptors

detect stretch in carotid arteries and aorta

if stretch is high

BP is high, the brain (medulla oblongata sends out impulses via parasympathetic neurones to SAN), slows the heart and causes vasodilation of arterioles, BP falls back to normal range

if stretch is low

BP is low, the brain speeds up the heart rate and causes vasoconstriction of arterioles

Capillary exchange

the exchange of substances (O2, nutrients, CO2) between the blood and tissues in the capillaries

Hydrostatic pressure

blood pressure forces fluid out of capillary containing nutrients and oxygen

Oncotic pressure

fluid carrying CO2 is drawn back into the capillary by osmosis due to higher concentration of protein solute (albumin)

What happens with excess tissue fluid

it gets taken up into lymph vessels and taken back to the veins near the heart so is added back into the blood circulation

Lymph contains

tissue fluid (water, ions, urea), lymphocytes, also lipids from digestion

function of lymph nodes

filter the lymph so they can detect any pathogens

Primary lymphoid organs

Thymus (site of T lymphocyte maturation and release) and Bone marrow (site of B lymphocyte development and maturation)

Secondary lymphoid organs

Tonsils (mostly made of lymphocytes, detect virus/bacteria entering through mouth), Lymph nodes (made mostly of lymphocytes, detect virus/bacteria in the lymph as it flows through), Spleen (made of red and white pulp, red pulp filters out old RBC, white pulp made of lymphocytes filters virus/bacteria from blood

Lymphadenitis

painful swollen lymph nodes, usually due to local infections

units used to measure blood pressure

mmHg

'normal' range of systolic and diastolic blood pressure

90/60 to 120/80