topic 1. the heart.

Systole definition

Phase of the heartbeat where the heart muscle contracts

Diastole

Phase of the heartbeat where beat where the heartbeat relaxes

Atrial systole

• two atria contract increasing blood pressure

• Increase in blood pressure causes the atrioventricular valves open and blood flows from atrium to ventricle

• Semilunar valves are closed

Ventricular systole

• ventricles contract increasing blood pressure

• Increase in blood pressure causes the atrioventricular valves closed to prevent backflow

• Increase in blood pressure causes semilunar valves open

• Blood moves from the ventricles to the aorta and pulmonary artery

Label the heart

Pathway of blood through the heart

Body - vena cava - right atrium - tricuspid valve (open) - right ventricle - semi lunar valve (open) + tricuspid valve (close) - pulmonary artery - lungs (blood becomes oxygenated) - pulmonary veins - left atrium - bicuspid valve (open) - left ventricle - semi lunar (open) + bicuspid (close) - aorta - body

Cardiac muscle

Made up of cells connected by cytoplasmic bridges, which enables electrical impulses to pass through the tissue. It contains large numbers of mitochondria and myoglobin molecules.

Key differences between arteries and veins

Veins have

• wider lumen

• Thinner walls

• Less collagen, smooth muscle and elastic fibres

• Valves

Veins and arteries similarities

Walls of both vessels contain collagen, elastic fibres and smooth muscle. Both have a lumen

What makes up inner layer of arteries and veins

• single layer of simple endothelial cells - flat + smooth so blood can flow

What makes up Middle layer of arteries and veins

• Circularly arranged elastic fibres and smooth muscle

What makes up outer layer of arteries and veins

Collagen

What is endothelium

A type of epithelium that lines the interior surface of blood vessels. It is a thin layer of simple squamous cells called endothelial cells

What are elastic fibres

Allows the vessels to stretch and recoil so they don’t rupture when pressure comes in. NOT contracting as doesn’t require energy/ATP

What is smooth muscle

For constriction and dilation - relaxes to allow more blood flow to area and contracts to restrict blood flow. (Vasoconstriction + vasodilation)

What is collagen

For strength and durability, flexible, connective tissue

Features of capillaries

• One cell thick

• Join arterioles to venules

• 10 micrometres in diameter

Network of capillaries explained

• blood pressure decreases as it moves from artery to arteriole to capillaries

• Capillaries are 1 cell thick which slows blood down so gas exchange can happen

• Once blood flows through capillaries its deoxygenated and moves into the venules and then veins

Why do veins have valves

• low blood pressure so blood can backflow and veins make sure blood flows in 1 direction

Haemolymph

= a fluid equivalent to blood in most invertebrates

What is diffusion

Movement of molecules from an area of high concentration to an area of ow concentration down a concentration gradient

Ficks law

Rate of diffusion is proportional to SA:V ratio x difference in conc / length of diffusion path

Open circulatory system

Consists of a heart that pumps haemolymph through short vessels and into a large cavity called haemocoel

Organism with an open circulatory system have:

• low metabolic rate

• Large SA:V

• = sufficient diffusion rate between haemolymph and cells of O2/CO2

Closed circulatory system

Blood is fully enclosed within blood vessels at all times

Organisms with closed circulatory systems:

• High metabolic rate + low SA:V

• generate high pressure so blood travels faster, more efficient transport system

• Overcomes limitations of diffusion

Single circulatory system

• 1 system

• Higher BP than no blood vessels BUT not too high to damage capillaries

• Not as efficient

Double circulatory system

• 2 systems

• Pump 1: low blood pressure in lungs to protect capillaries in lungs

• Pump 2: boosts the blood pressure for rapid and effective delivery of oxygen/glucose