Transport in Animals Flashcards
why is there a need for specialised systems in multicellular organisms?
- high metabolic demand=diffusion alone x effective
- ↓SA:V in large multicellular organisms=↓SA for absorption
- enzymes/hormones need to be transported
- food digested has to be transported to every cell
- waste products removed from every cell and transported to excretory system
open vs closed circulatory system
open eg. insects+molluscs:
* few vessels
* pumped from heart into body cavity (haemocoel)
* low pressure
* direct contact with blood and cells
* open ended vessel returns fluid to heart
* haemolymph transports nutrients/waste
* heart in thorax+abdomen
* no steep conc. gradient
* x meet demand of organism
closed eg. annelids (worms), vertebrates:
* blood enclosed in vessels=x direct contact with cells
* heart pumps under pressure
* substances enter and leave by diffusion
* bld. flow adjusted (widening/narrowing)
* contain bld. pigment for gases
* single or double
single vs double circulatory system
single eg. fish, annelid
* bld. travels once through heart
* bld. passes through 2 srts of capillaries to exhange gases, nutrients, waste
* pressure drops limits efficiency (exception fish=cold blooded, weight supported by water & countercurent
double eg. birds, mammals
* blod. travels twice through heart
* most efficient
* high pressure
* fast flow
* effective for active animals that manitin body temp.
layers of blood vessels
- tunica externa/adventitia
- tunica media
- tunica intima
histology of vessels
- elastic fibres:provide flexiblity, stretch, recoil, thin+interwoven with collagen fibres (prevent tearing), made of elastin
- collagen fibres: high tensile strength, structural support, some flexibility (fibrous protein)
- smooth muscle: contracts/relaxes=constricts/dilates artery
- endothelium:inner lining of cells, folds/unfolds, single layer, smooth=↓ friction
histology of arteries
- lined with endothelium (tunica intima)
- thick muscular (tunica media) walls=withstand+maintain ↑ pressure
- wall has smooth muscle (tunica externa)
structure+function of arterioles
- diameter (<100 μm)
- come from an arterial branch (between small arteries+capillaries)
- lined with smooth muscle (less elastin)=allows diameter to be controlled by nerves+hormones
- dilate/constrict=control blood flow
- smooth muscle contracts=vasoconstriction+↑ pressure&resistance
structure and function of capillaries
- diameter=same as rbc=only one can pass at a time=slows down bld. flow=allows fro diffusion to occur
- one cell thick=thin walls=short diffusion path
- links arterioles+venules
- gaps b/w flattened endothelial cells (except brain)=leaky walls=allows substances to enter/exit
- arranged into capillary beds=large SA
- site of exchange+diffusion of materials b/w cells+bld as ↓bld. flow
structure+function of venules
- thin walls+little smooth muscle
- receive bld from capillaries
- loads join to form a vein
structure+function of veins
- diameter (<30μm-2.5cm)
*carry bld away from cells, towards heart
*↓pressure, no pulse=can act as large resrvoirs - deoxygenated bld except from pulmonary+umbilical vein
- outermost layer=lots of collagen but little elastic fibres
- wide lumen+smooth endothelium
- valves=folds of innermost layer+strengthened by fibrous tissue=prevent back flow, only found in medium/small veins
- close to muscles in limbs=muscle contracts=press on bld in veins+push it up
- breathin movements in chest=act as a pump to pull bld up
Components and functions of blood
-
components
Plasma (mostly water, transports substances in solution), rbcs (carry O2), wbcs (immunity), platelets (clotting) -
functions of bld
Transports O2, CO2, nutrients from digestion, waste from excretion, hormones, etc
Tissue fluid: how is it made+role
- has same composition as plasma but it has no rbcs, less proteins, less wbcs
-
formation
At the arteriole end of capillaries:
A high hydrostatic pressure, exerted by the force of the heart pumping, forces fluid out of capillaries.
This forms tissue fluid surrounding body cells.
At the venule end of capillaries:
The hydrostatic pressure is lower.
Proteins in blood exert a high oncotic pressure in capillaries.
The water potential is lower in capillaries than in tissue fluid due to fluid loss.
Some tissue fluid moves back into capillaries by osmosis.
Lymph: composition+formation+transport
- same as tissue fluid but has less oxygen+nutrients, more fatty acids, more wbcs
- the tissue fluid that doesn’t reenter capillaries=drains into lymph vessels=forms lymph
- transported through lymph vessels by muscle contractions
- lymph passes lymph nodes=filter pathogens
- lymph eventually returns to bld
Structure of heart
-
separate pumping mechanisms
Bld pressure drops in lungs as it flows in capillaries
Single pump=slows bld flow to body cells
2 pumps increase pressure before bld circulates -
valves
AV valves=tricuspid valve (right)+bicuspid/mitral valve (left)
Semi-lunar valves
Found in aorta and pulmonary artery
Cardiac cycle
-
atrial systole
Atria contract (ventricle relax)=up atrial pressure=AV valve open=bld flows into ventricles -
ventricular systole
Ventricles contract (atria relax)=up ventricular pressure=semilunar valves open+AV valves close=bld flows into arteries (aorta+p.artery)
-diastole
Ventricles+atria relax=SL valves close=bld flows passively into atria
