Lecture 4 & 5: Respiratory & Circulatory Physiology Flashcards
What is respiration?
- Cellular respiration: oxidation of food (e.g. glucose) to generate ATP. Energy production via aerobic metabolism. (End goal of getting O2 in body, but not gonna cover)
- External respiration: gas exchange , O2 from external environment (air/H2O), lungs, through circulatory system, to cells.
External respiration
Functions:
1. O2 uptake & CO2 excretion
2. pH regulation
Types of gas movement:
- exchange via diffusion: 1. between respiratory surfaces, alveoli in lungs, O2 diffusing from lungs into bloodstream. 2.from blood into cell.
- bulk transport: 1.movement of external media = ventilation, breathing air into lungs or movement of H2O (fish) across respiratory surface (gills). 2. During circulation, transport of O2 & CO2 in circularly fluid.
How fast does diffusion occur?
Fick’s Law of Diffusion:
- adaptations that speed up diffusion
- e.g. alveoli cells in lungs (unit of gas exchange), airflow entering the lungs/alveoli, rich in O2, O2 diffusing into capillary which circles the alveoli & CO2 being removed. This happening by diffusion.
- R = rate of diffusion, D = diffusion constant (equal to R) (specific for each molecule, for O2 it ^ if dissolved in H2O, which is why gas exchange surfaces are moist), A = area over which diffusion occurs, ΔP = pressure difference between 2 sides (^concentration gradient^rate of diffusion), d = distance over which diffusion occurs (thickness of membrane).
Adaptive respiratory physiology
- Insect: spiracles & tracheal system (directly deliver O2 to respiring tissues)
- Bird: air sacs (maintain direction of flow)
- Fish: respiratory exchange across gill
Aim of all gas exchange surfaces is to improve rate of gas exchange
Gas exchange surfaces
Characteristics of gas exchange surfaces: permeable to gases, moist (dissolved O2 ^rate), thin & maximise SA
Gas exchange surfaces: CUTANEOUS RESPIRATION (skin breathers)
- O2 diffuse across skin.
- e.g. flatworm, small, aquatic, few cells thick.
- e.g. earthworm, need to stay moist (or suffocates) so excrete mucus & bury themselves in damp soils, but larger so has circulatory system, skin is 1 cell thick, gases diffuse across & diffuse into dense network of capillaries & into circulatory system.
- e.g. reptiles, scales impair O2 transport across skin, but do still undergo skin breathing
Gas exchange surfaces
Water-breathers: external evaginated gills, in fish & crustaceans they protected, fish has bony flap that covers gills, crustaceans have carapace, gills can be big & complex as supported by H2O.
Air-breathers: invaginated lungs or tracheae, need to keep respiratory gas organs moist so internal or invaginated, need advanced structural system for gas exchange organs.
Water & skin breathing
- over 200 species of amphibian fish can breathe by H2O & air.
- e.g. mangrove killifish
- huge plasticity in this organ
- gene expression and structural changes in skin to do with remodelling of the skin in order to skin breath, reduces thickness of skin, more permeable to H2O & dissolved O2, over a few days will cause reduction in amount of collagen in skin so more permeable to O2 .
Water and air breathing
- tadpoles are aquatic but adult frogs spend lots of time breathing air.
- in tadpoles gills & skin are important in uptaking O2, as moves through metamorphosis & becomes adult gills diminish, lungs develop but skin also important in uptaking O2. BUT different when comes to CO2 excretion, excrete most CO2 by skin.
How is gas exchanged achieved?
- Simple diffusion (e.g. flatworm), skin breather
- Convection of external medium only: cnidarians(e.g. jellyfish, corals) & sponges, which use flagella/tentacles to circulate surrounding H2O in order to absorb O2 (&nutrients)(no circulatory system), sponge has series of osculum pores which moves tentacles to draw H2O across body surface & out through pore, that movement if the H2O is allowing diffusion of O2 into tissues.
- Convection of internal medium only: e.g. earthworm = skin breather & circulatory system, is convecting O2 within body (in circulatory system)
- Convection of internal & external media: animals that ventilate (move external medium, air/H2O) also have circulatory media which will circulate O2 in bloodstream.
Challenges for Water breathers
- High viscosity & density: H2O is 850x more viscous than air, high viscosity of H2O slows down diffusion of gases through gills (& requires more energy), fish evolved specialized respiratory structures, e.g. gills with thin & delicate filaments. The large surface area & thin structure facilitate efficient gas exchange despite high viscosity of H2O.
- Low O2 solubility: a) limited amount of dissolved O2 impact respiratory efficiency, BUT large SA of gills, Countercurrent Exchange Mechanisms, O2-deprived blood moves through gill filaments, it exposed to oxygenated H2O, O2 diffuses from H2O into blood,CO2 diffuses from blood into the H2O, maximises O2 uptake.
- Low diffusion rate:
Diversity in aquatic invertebrates
- Gills: Crustaceans (e.g., Crabs, Shrimp, Lobsters): gills located in branchial chambers or appendages, & H2O is circulated over gill surfaces to facilitate gas exchange. Mollusks (e.g., Clams, Mussels): gills extract O2 from H20, use cilia to bring H2O over the gills.
Fish gills
A) Active Bicarbonate Pump: CO2 converted to carbonic acid (H2CO3) in blood, H2CO3 dissociates into bicarbonate ions (HCO3-)& hydrogen ions (H+), on basolateral membrane (the side facing the blood) of gill epithelial cells, HCO3- pump actively transports HCO3- out of gill epithelial cells into blood, to maintain electrochemical balance, chloride ions (Cl-) move into gill epithelial cells, compensating for export of HCO3-, on the apical membrane (the side facing the gill’s external environment), HCO3- are transported across membrane & released into surrounding H2O.
B) Ram ventilation: in some fish, use forward movement through H2O to maintain continuous flow of oxygenated H2O over their gills.
Fish gills
Structure:
1. Operculum: protective bony flap, shields & supports gill, pair on each side of head, helps control H2O flow over gills.
2. Gill Arches: support gill filaments, in pairs on each side of head.
3. Gill Filaments: thin projections, extend from gill arches, primary sites for gas exchange between blood & surrounding H2O, covered in respiratory epithelium, contain network of capillaries.
4. Gill Lamellae:Gill filaments subdivided into smaller structures= gill lamellae,^ SA for gas exchange, covered in thin layer of epithelial cells, close proximity of H2O& blood in lamellae allows for efficient diffusion of gases.
Fish gills
Countercurrent flow maximises gas exchange
- maximizes gas exchange efficiency
- lamellae ^ SA for gas exchange.
- flow of H2O over the gill filaments & flow of blood within the filaments occur in opposite directions.
- ensures O2 concentration in H2O remains ^ than O2 concentration in blood & CO2 concentration in blood is ^ than in H2O, facilitating efficient removal.
