MODULE 3 OCR A level Biology

Features of exchange surfaces

Thin

Ability to maintain a steep concentration gradient

Large surface area to volume ratio

Moist lining

Features of the nasal cavity

Large surface area

Good blood supply - warms air to body temperature

Ciliated epithelium cells waft/move mucus back up to the trachea to be swallowed

Goblet cells secrete mucus to trap microbes and dust to prevent infection; also prevents dehydration.

Moist

Warms and moistens air before it enters the lungs

Trachea

Wide tube, main airway from nose to chest, supported by cartilage rings to prevent collapse

Lined with ciliated epithelium, walls contain smooth muscle and elastic fibres

Cartilage in the trachea

Strong and inflexible, strength to prevent collapse during inhalation.

Rings are incomplete to allow space for the food to pass down the oesophagus

Support larger bronchioles

Bronchi

The passages that direct air into the lungs

Features of bronchioles

Bronchioles contain smooth muscle walls - when this contracts, bronchioles dilate, and the volume of air changes; they also elastic fibres.

Bronchioles are lined with a thin layer of ciliated epithelium for gas exchange, but usually don't contain goblet cells

Not usually supported by cartilage; small bronchioles have no smooth muscles

Alveoli

Tiny air sacs, main gas exchange surfaces of the body, coming from bronchioles

Features of alveoli

Layer of thin, flattened epithelial cells

Elastic fibres which allow elastic expansion and returning to resting size

Large surface area due to there being many

Good blood supply from capillaries

Thin walls of alveoli and capillaries minimises diffusion distance

Good ventilation maintains concentration gradient

Inner surface covered by a thin layer of water, salts, and lung surfactant so it can remain inflated and assist oxygen diffusion

Ventilation

Movement of air in the lungs as a result of pressure changes in the thorax due to breathing

Thorax

Pleural cavity, chest

Pleural membranes

Thorax is lined by pleural membranes which surround the lungs

Space between is the pleural cavity, filled with lubricating fluid so that membranes slide easily over each other when breathing

Inhalation

External intercostal muscles contract. Ribs move outwards and upwards.

Diaphragm contracts, flattening and lowering.

Thorax volume increases, and pressure decreases lower than atmospheric air.

Air is drawn in to equalise pressure.

Moves into alveoli and elastic fibres stretch.

Exhalation

External intercostal muscles relax, returning to orginal shape, ribs move downwards and inwards.

Muscles of diaphragm relax, moves into resting dome shape.

Thorax volume decreases, pressure increases above atmospheric air.

Air leaves lungs to equalise pressure.

Elastic fibres in alveoli recoil to assist this.

Forced exhalation

Internal intercostal muscles contract to pull the ribs down and inwards hard and fast.

External intercostal muscles relax.

Abdominal muscles contract to force the diaphragm up, increasing lung pressure quickly.

Asthmatic attack

Cells lining bronchioles release histamines - become inflamed and swollen.

Excess mucus produced

Bronchiole walls contract

Airways narrow and fill with mucus, increasing difficulty of breathing.

Tidal volume

Amount of air exchanged in a single breath

Vital capacity

Maximum volume of air exchanged in a single breath

Residual volume

Volume leftover from exhaling

Inspiration reserve

Extra volume able to be filled from inhaling

Expiration reserve

Extra volume able to be released from exhaling

Ghost air

Air elsewhere in the ventilation system e.g. bronchi

How is lung capacity measured?

Using a spirometer

How the spirometer works:

When you exhale, the chamber rises, and when you inhale, the chamber falls.

Attached to a pen, therefore a graph is drawn.

CO2 scrubber removes CO2 from recirculated air

Total air breathed per minute

Tidal volume x breathing rate

Breathing rate

number of breaths per minute

Oxygen consumption

Gradual removal of carbon dioxide, lowering the volume via a gradient

Common tidal volume

500cm^3

Common vital capacity

4-4.5dm^3

What is ventilation necessary for?

Gas exchange in the alveoli - CO2 into the alveoli from the blood, and O2 from the blood into the alveoli

What is involved in ventilation?

Intercostal muscles (lie between the ribs)

Diaphragm

Work together to change volume of the thorax, changing lung air pressure, inducing inspiration/expiration

Which breathing process requires energy?

Inhalation

Why do insects have specialised gas exchange?

Very low surface area to volume ratio compared to smaller organisms

Tough exoskeleton that largely inhibits gas exchange

Don't usually have haem groups in blood to carry oxygen.

Instead developed to deliver oxygen and remove CO2 directly from cells

What are spiracles?

External openings to the respiratory system along the exoskeleton, allowing for gas exchange

Sphincters open and close these spiracles

Spiracles lead to tracheae

What do sphincters do?

Open and close spiracles to prevent water loss due to vapour (produced from moist walls/tracheal fluid)

Usually closed during inactivity, but open due to increased CO2 levels or oxygen demand.

Tracheae (insects)

Direct air to tissues in insects

Moist walls for gas diffusion

Lined by spirals of chitin to prevent them from closing (like cartilage) which is relatively impermeable to gas

Branched into narrower tracheoles

Tracheoles (insects)

Narrow and abundant - large SA

Lack chitin - more permeable to gases

Tracheal fluid allows gases to dissolve before gas exchange.

Spread between cells for gas exchange and short diffusion system.

How do insect respiratory systems respond to oxygen demand increase?

Lactic acid is produced more in cells, lowering cell water potential

Water from tracheal fluid exits tracheoles

More surface area exposed for gas exchange/decrease of diffusion distance, drawing air into tracheoles via diffusion gradient

Mechanical ventilation of insects?

Bulk movement - Air is actively pumped into the system by muscular pumping movements of the thorax/abdomen

Changes volume of the body and pressure in tracheoles, drawing air in/out

Squeezes air from air sacs into tracheoles.

Collapsible enlarged trachea in insects?

Act as air reservoirs, increase the amount of air moved through the gas exchange system

Inflated/deflated by ventilating movements of the thorax and abdomen/movement of wings

Insect oxygen supply methods

Tracheal tubes - passive diffusion

Mechanical ventilation

Collapsible enlarged trachea

Operculum?

A bony flap that contains gills in an opercular cavity and covers these for protection

Adaptations of fish gills?

Lots of layers and lots of folded lamellae -> large surface area

Short diffusion path

ascularised and ventilated

Counter current blood flow in fish

Low oxygen blood enters the capillaries

Water passes over from the opposing direction of blood flow

Oxygen from water diffuses into the blood.

The concentration gradient is high because oxygenated blood is constantly removed

This high oxygen water than exits the gills

Tips of adjacent gill filaments overlap to increase resistance to water flow, and slow down movement

Stages of gill ventilation

The mouth opens to take water in

The buccal cavity floor is lowered, increasing the volume for water and decreasing pressure compared to outside

Water rushes in down pressure gradient. Mouth is shut

The opercular cavity expands, increasing volume and decreasing pressure

The buccal cavity floor is raised, increasing pressure compared to the opercular cavity, so water moves over the gills to the opercular cavity

The operculum opens and the sides of the opercular cavity move inwards to increase pressure.

Water rushes out through the operculum

Haemolymph?

Insect transport medium

Transports food, nitrogenous waste products, but NOT products of gas exchange

Haemocoel?

Insect body cavity

Why do multicellular organisms need specialised transport systems?

Increased metabolic demand

Smaller SA:V ratio, larger organisms

Hormones and enzymes are produced away from target cells

Removal of waste products

High oxygen demand

Open circulatory systems?

Low pressure

Haemolymph directly pumped into haemocoel, directly contacting tissues and cells.

Collected by drain-like open vessels to return fluid to heart

Seperate to gas exchange system

Closed circulatory systems?

Blood is pumped at high pressure that can be altered by vasodilation/constriction

Blood remains within the vessels and materials diffuse via capillaries

Veins carry blood to the heart; arteries carry from heart

The circulatory system also carries nutrients, gases, and waste products

Single circulatory system?

Blood only flows through the heart once for each circuit of the body

At the first capillary, O2 and CO2 are exchanged; at the second, substances are exchanged between blood and organ systems

Low pressure and low rate

Fish* and worms

Double circulatory system?

Greater pressure and flow rate

Four heart chambers

Elastic fibres?

Present in all lung tissues

Composed of elastin; stretch and recoil to allow flexible vessel walls

Recoil makes expiration a passive process

Smooth muscle?

Found throughotu the walls of the bronchi and bronchioles

Contract and relax to change lumen size therefore blood pressure/amount of air

Collagen?

Provides structural support to maintain vessel's shape and volume

Endothelium?

Smooth for easy flow

Features of arteries

Small lumen

Large muscular wall (more elastin than veins)

High pressure, pulse

No valves

Oxygenated blood from the heart*

Features of veins?

Wide lumen

Thin wall of muscles (less collagen and less elastic muscle than arteries)

Low pressure

Valves

Deoxygenated blood to the heart*

Found between big active body muscles - muscle contraction moves blood

Closer to the surface than arteries

Thin walls may distend/bulge

Features of capillaries?

Tiny lumen 1RBC thick

Thin wall of endothelium

Low pressure

No valves

Network supplies muscles with oxygen and nutrients for respiration; remove respiratory waste like CO2

Gaps between endothelial cells allow substances to leave in tissue fluid

Adaptations of capillaries

Large surface area

Larger total cross sectional area compared to arterioles means blood flow falls, allowing more time for diffusion of substances

Features of arterioles

Connect arteries and capillaries

More smooth muscle for vasoconstriction and vasodilation

Blood flow journey:

Lungs -> pulmonary veins -> left atrium -> left ventricle -> aorta -> body -> vena cava -> right atrium -> right ventricle -> pulmonary artery -> lungs

Oncotic pressure?

Tendency of water to move into blood from tissue fluid by osmosis

NEGATIVE

Hydrostatic pressure?

Pressure generated by a heart contracting to move water out of the plasma

POSITIVE

Tissue fluid?

Similar to plasma, lacks erythrocytes and plasma proteins

Vector for substances in blood to diffuse to cells

Lymph?

Similar to plasma, less oxygen and nutrients

Contains fatty acid

Tissue fluid that isn't reabsorbed (10%) drains into lymph capillaries to become lymph

Tissue fluid formation

Plasma proteins lower blood water potential, so water tends to move in by oncotic pressure. However, blood flow from the arterioles is under pressure for contraction - this is hydrostatic pressure - so this outweights oncotic pressure and forces plasma out to form tissue fluid.

Hydrostatic pressure falls at venule end, so oncotic pressure reabsorbs plasma.

Lymphatic system?

Lymph capillaries join up to form larger vessels - similar to veins, have valves and transport via muscle contraction.

Lymph returns to the blood via subclavian veins

Lymph nodes along lymph vessels are where lymphocytes build up.

Major in body's defence mechanism - enlarged lymph nodes are due to them intercepting bacteria

Positive cooperativity of haemoglobin

How the haemoglobin molecule changes shape each time to optimise bonding with oxygen molecules

Specialisation of erythrocytes

Transport oxygen around body. Flattened biconcave shape increases surface area to volume ratio optimising diffusion of oxygen into cell. Contain haemoglobin to carry oxygen. No nucleus or many other organelles increasing space for haemoglobin. Flexible so can squeeze through narrow capillaries.

Haemoglobin + oxygen ⇌

oxyhaemoglobin

Hb + 4O2 ⇌ Hb(O2)4

Forming Hb(O2)4 maintains a diffusion gradient of oxygen into the cell

Haemoglobin at low ppO2

Haemoglobin has a low affinity for oxygen

25% saturation at Kpa

Haemoglobin at higher ppO2

When an oxygen has binded, haemoglobin's quaternary structure changed to increase affinity of haem group for O2 - small increases in pp increases affinity.

At 7kpa, 75% saturation

Fourth oxygen (Hb)

Takes a large partial pressure to take up O2 due to the unlikeliness of collision

Often offloads in areas of significantly low pressure such as heavily respiring tissue

Haemoglobin oxygen affinity curve

Where does haemoglobin unload and offload oxygen?

Haemoglobin takes in O2 at areas of high ppO2 - primarily the alveoli where it also offloads CO2

Haemoglobin unloads in areas of low ppO2 - high aerobic respiration such as tissues and cells

The Bohr Effect

At areas of high ppCO2, the oxygen dissociation curve shifts to the right, decreasing haemoglobin's affinity for oxygen. (this is due to the dissociation into H+ ions)

Hydrogen ions react to form haemoglobinic acid to prevent the build up of hydrogen ions and act as a buffer

It changes shape so that more oxygen is released when needed.

Chloride shift

The movement of chloride ions into erythrocytes while hydrogen carbonate ions move out into blood plasma, to maintain the cell's electrical balance

How can CO2 be transported in the blood?

5% dissolved in the plasma.

10-20% combined with amino groups in polypeptide chains of haemoglobin to form carbaminohaemoglobin.

75-85% converted into hydrogen carbonate ions in the cytoplasm of erythrocytes.

Carbon dioxide in the blood (equation)

Carbon dioxide + water ⇋ carbonic acid ⇋ hydrogen carbonate + hydrogen ions

CO2 + H2O ⇋ H2CO3 ⇋ H+ + HCO3-

What does haemoglobin form with H+?

Haemoglobinic acid, to act as a buffer and avoid changing haemoglobin pH

Erythrocytes at respiring cells (CO2)

Negative hydrogen carbonate ions diffuse out of the RBC via a gradient.

Chloride shift occurs to balance this.

Because CO2 is constantly converted to H2CO3, there is a diffusion gradient maintained into the cell. Carbon dioxide is able to be removed due to this

Erythrocytes at the lungs (CO2)

Hydrogen carbonate ions diffuse back into RBC and reform carbonic acid, this is then broken down into CO2 and water (and catalysed by carbonic anhydrase)

This releases CO2 which diffuses out of the lungs to be respired

Chloride ions also diffuse out.

How do fetus' gain O2?

The mother's oxygenated blood runs close to the deoxygenated fetal blood in the placenta.

Maternal blood has higher O2 concentration, so it diffuses into fetal blood.

How is efficiency of O2 diffusion into fetal blood increased?

Fetal haemoglobin has a slightly higher affinity for oxygen.

Fetal haemoglobin has two different polypeptide chains which cause O2 affinity to increase

Carbon dioxide from fetal blood diffuses into maternal blood, lowering the maternal haemoglobin's oxygen affinity

Vena cava?

Superior - receives blood from the upper body and head

Inferior - receives blood from the lower body

Tricuspid valve?

Between the right atrium and ventricle, preventing back flow

Bicuspid valve?

Between the left atrium and ventricle, preventing back flow

Semilunar valve?

Between the right ventricle and the pulmonary artery; also between the left ventricle and the aorta, preventing backflow

Septum?

Divides the left and right chambers of the heart, preventing mixing of deoxygenated and oxygenated blood

Cardiac cycle?

Events in a single heartbeat

Tachycardia?

Overly rapid heartbeat

Bradycardia?

Abnormally slow heartbeat

Ectopic heartbeat?

Extra heartbeats that are out of the normal rhythm.

Atrial fibrillation?

Rapid, random, ineffective contractions of the atrium

Coronary arteries?

Blood vessels that branch from the aorta and carry oxygen-rich blood to the heart muscle

Movement of deoxygenated blood?

Deoxygenated blood enters the right atrium from the vena cava at low pressure.

As blood flows in, pressure builds up until atrial pressure>ventricular pressure, so the tricuspid valve opens and blood enters the ventricle.

Atrial systole occurs to push remaining blood into ventricles.

This causes ventricular systole. Pressure in ventricles rises rapidly, when ventricular pressure>atrial pressure, the tricuspid valve closes to prevent backflow, but semi-lunar valve opens (atrial diastole happens)

The right ventricle contracts fully and pumps deoxygenated blood through semi-lunar valves into the pulmonary artery, which transports it to the capillary bed of the lungs.

Ventricular systole reduces ventricular pressure below that of the pulmonary artery, so semi-lunar valves shut.

Movement of oxygenated blood?

Oxygenated blood enters from the pulmonary vein at low pressure.

As blood flows in, pressure builds in the left atrium until atrial pressure>ventricular pressure. The bicuspid valve opens and atrial systole occurs to push all blood into the left ventricle.

This causes ventricular systole, and ventricular pressure rises rapidly. The bicuspid valve closes to prevent backflow, and semi-lunar valves open. (atrial diastole occurs)

The left ventricle contracts fully and pumps oxygenated blood through semi-lunar valves to aorta and the body.

Ventricular diastole occurs. When the ventricular pressure

SAN?

Site of pacemaker that iniates heartbeats

Found at the top of the right atrium

AVN?

Found near the semi-lunar valve, next to septum

Picks up SAN impulses and stimulates bundle of His

Bundle of His?

Bundle of conductive tissue made up of Purkyne fibres which penetrate through the septum between ventricles