Transport in Animals

Question 1

why is there a need for specialised systems in multicellular organisms?

Answer 1

• 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

Question 2

open vs closed circulatory system

Answer 2

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

Question 3

single vs double circulatory system

Answer 3

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.

Question 4

layers of blood vessels

Answer 4

• tunica externa/adventitia
• tunica media
• tunica intima

Question 5

histology of vessels

Answer 5

• 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

Question 6

histology of arteries

Answer 6

• lined with endothelium (tunica intima)
• thick muscular (tunica media) walls=withstand+maintain ↑ pressure
• wall has smooth muscle (tunica externa)

Question 7

structure+function of arterioles

Answer 7

• 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

Question 8

structure and function of capillaries

Answer 8

• 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

Question 9

structure+function of venules

Answer 9

• thin walls+little smooth muscle
• receive bld from capillaries
• loads join to form a vein

Question 10

structure+function of veins

Answer 10

• 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