H.1.1

What are hormones?

Chemical messengers that are secreted by endocrine glands into the blood and are transported to specific target cells.

H.1.2

What are the three different types of hormones?

Steroids

Hormones

Tyrosine derivatives

H.1.3

What is the mode of action of a steroid hormone?

They can pass through the cell membrane

Bond with a  receptor protein within the cell to form a hormone-receptor complex.

 This complex goes into the nucleus and binds to certain genes 

this can either inhibit or induce transcription

The biochemistry of the cell is dramatically altered.

H.1.3

What is the mode of action of a peptide hormone?

Hormone binds to a receptor on the outside of the cell (glycoprotein)

This causes a secondary messenger to be released which causes the cell activities to change by activating or inhibiting enzymes.

H.1.4

What is the relationship between the pituitary gland and the hypothalamus?

It connects the nervous system with the endocrine system

The hypothalamus controls the pituitary gland (each lobe in a slightly different way)

Posterior lobe - contains the axons of neurosecretory cells, Hormones are made in the cell body located in the hypothalamus and then they move down the cell into the pituitary gland, 

Anterior lobe - uses a portal vein to collect hormones made in the hypothalamus

H.1.5

How is the secretion of ADH controlled?

By a negative feedback mechanism.

The hypothalamus is sensitive to changes in plasma concentration.

When there is little water in the blood it is detected by the hypothalamus.  This sends a signal to the posterior lobe of the pituitary gland which releases ADH.

ADH stimulates more water to be retained thus increasing the levels of water in the blood so that the hypothalamus no longer sends impulses to the pituitary gland

H.2.1

How and where are digestive juices secreted?

H.2.2

What are the structural features of exocrine gland cells?

Lots of RER (for protein secretion)

Many ribosomes - to make proteins for secretion

Golgi bodies

vesicles

Lots of mitochondria for active transport

group around the end of a duct

This arrangement is known as an acinus

H.2.3

What is the composition of Saliva?

mucus - lubricant

amylase - helps to digest starch

Water - solvent

H.2.3

What is the composition of gastric juice?

Hydrocholoric acid

Pepsin

water

Mucus

H.2.3

What is the composition of pancreatic juice?

water

trypsin

lipase

amylase

high concentrations of bicarbonate ions

H.2.4

How is the secretion of gastric juice controlled?

When the brain perceives food it sens impulses to the stomach so that it starts producing digestive juices.

Once food is in the stomach, receptors send send sensory signals to the brain.

The brain responds by causing the secretion of even more gastric juice

The presence of polypeptides and the distension of the stomach causes the release of the hormone gastrin

Gastrin stimulates the production of HCl

H.2.5

What is the role of membrane-bound enzymes on the surface of epithelial cells in the small intestine?

Active sites of these enzymes face the lumen of the small intestine.

This means that the products of these enzymes are immediately available for absorption.

H.2.6

Why is Cellulose not digested in the alimentary canal?

Cellulose is a polysaccharide that needs to be broken down by the enzyme cellulase.

Humans do not have this enzyme.

Certain herbivores such as sheep and cows have bacteria in their gut which produce the enzyme cellulase so that cellulose can be digested.

H.2.7

Why are Pepsin and Trypsin initially synthesized as pepsinogen and trypsinogen?

So that they only digest the proteins that need to be digested (i.e. not the stomach wall etc.)

Pepsin is activated by HCl in the stomach and Trypsin is activated by enterokinase in the small intestine

They are activated by the removal of additional amino acids.

H.2.8

What causes the development of stomach ulcers and subsequently stomach cancer?

Most bacteria can't survive in the stomach because of the acid.

Helicobacter Pylori lives in the lining of the stomach so that the acid doesn't reach it.  When the immune system detects the infection white blood cells are sent to the area but they can't penetrate the lining because of the mucus layer.  A build up of white blood cells causes an ulcer

H.2.9

What is the role of bile in Lipid digestion?

Bile emulsifies lipids - makes it into many smaller droplets

this increases the surface area

the enzyme Lipase in water soluble and can only work on the Lipid-Water interface

H.3.1

Draw and label a transverse section of the Ileum as seen under a light microscope.

H.3.2

What are features of the epithelial cells of a villus?

Microvilli - to increase surface area

Lots of mitochondria - for active transport

Pinocytotic vesicles  - as another form of active transport

Tight junctions between the cells - This means that only some things can be absorbed from the small intestine.

H.3.3

What mechanisms are used by the small intestine to absorb and transport food?

Facilitated diffusion - 

Active transport - 

Pinocytosis - 

H.3.4

What materials are egested and not absorbed?

Bile pigments

lignin

cellulose

Bacteria

Intestinal cells

H.4.1

How does blood circulate through the liver?

Oxygenated blood is brought to the liver by the hepatic artery.  The hepatic vein carries deoxygenated blood away from the liver.  The hepatic portal vein carries blood from the gut to the liver.  This transports substances directly.

Within the liver the blood flows through sinusoids

H.4.2

How does the liver control levels of nutrients?

an example is glucose

Many things are stored in the liver and is released when levels are low

H.4.4

What does the liver synthesize?

plasma proteins and cholesterol

H.4.6

How are erythrocytes and haemoglobin broken down in the liver?

The cell membrane of erythrocytes ruptures to release haemoglobin

this is absorbed by phagocytosis of the kupfer cells in the sinusoids - split into Haem + globin

Globins are hydrolysed to amino acids which are returned to the blood.

The Iron is removed from the Haem group and leaves behind bilirubin - bile pigments - these are released into the blood

The iron goes to the bone marrow to be used in the production of haemoglobin and the bilirubin is used in making bile in the liver.

H.4.7

How does excessive alcohol consumption damage the liver?

The liver breaks down alcohol and forms acetylaldehyde and NADH

this can combine with other proteins and interferes with their functioning

an excess of NADH causes a build up of lactic acid and a build up of fat in the liver

H.5.1

What are the events of the cardiac cycle?

atrial diastole

atrial systole

ventricular diastole - dub sound

ventricular systole - lub sound

H.6.1

What is partial pressure?

The pressure exerted by each of the gases in a mixture of gases

H.6.2

What does the oxygen dissociation curve of adult human haemoglobin mean?

the s-shaped curved shows how the affinity of haemoglobin for oxygen increases as the haemoglobin gains more oxygen molecules.  This is seen as the partial pressure of oxygen increases.

H.6.2

What does the oxygen dissociation curve of foetal haemoglobin mean?

H.6.2

What does the oxygen dissociation curve of myoglobin mean?

Myoglobin can only hold one oxygen molecule and its purpose is to store oxygen in the muscles.  This essentially creates a back-up reservoir.  This means that at very low partial pressures of oxygen, myoglobin will give up its oxygen to prevent the onset of lactic acid production.

H.6.3

How is carbon dioxide carried by the blood?

Some is bound to Hb

a little dissolves in the plasma

most of it enters the red blood cells, is converted to HCO3- and then goes into the plasma

Within the red blood cells carbonic anhydrase, in the presence of water, turns CO2 into H2CO3 which is then split into H+ and HCO3-

H.6.3

What is the chloride shift?

This is when HCO3- from the red blood cells enters the blood plasma and is replaced by Cl- ions.

This maintains a balance of charges

H.6.3

What does carbonic anhydrase do? (and where?)

In the red blood cell

in the presence of water

it turns carbon dioxide into H2CO3 and then splits that into H+ and CO3-

H.6.4

What is the Bohr shift?

when carbon dioxide partial pressure is high, haemoglobins affinity for oxygen decreases

one such environment is tissues that are undergoing respiration, this means that high CO2 concentrations induce haemoglobin to release oxygen.

This is called the Bohr Shift and occurs when CO2 binds to Hb and changes its shape so that it has less affinity for oxygen

H.6.5

Why does ventilation rate vary with exercise?

When muscles are being used, more energy is needed, more ATP is needed, so more oxygen is needed and more CO2 is produced

In order to cope with this increased requirement ventilation increases

increased carbon dioxide levels and increased pH are detected by the brain to cause this

H.6.6

What are possible causes of Asthma? 

people can have a genetic predisposition

environmental triggers include:

allergens

certain arthropods

smoke

scented products

excercise - increased respiratory rate

some medications

cold air 

H.6.6

What are the effects of Asthma on the gas exchange system?

affects the airways to the lungs including - bronchi and bronchioles

airways become inflamed and swollen and often produce excess mucus

H.6.7

Why is gas exchange at high altitudes a problem?

Decreased air pressure at high altitudes

in less dense air diffusion of oxygen across the membrane of the alveoli is less efficient

this means that less oxygen enters the bloodstream

can cause altitude sickness

H.6.7

How does the body acclimitize to breathing at high altitudes?

At first the body compensates by increases heart rate and ventilation rate

no. of erythrocytes and haemoglobin increases

increase in capillaries in lungs and muscles

increase in lung size and surface area 

increase in myoglobin within tissues