3.12 understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics

Oestrogen
Stimulates the secondary sexual characteristics in women. For example, hair on underarms and around pubic area, a womens hips may widen, the development of breasts, the start of menstruation.

Testosterone

Stimulates the secondary sexual characteristics in men. For example,
 they will grow extra air on their face and body, their muscles will develop, they will begin to produce sperm, their voice will deepen and their penis and testes will enlarge.

3.11 understand how the developing embryo is protected by amniotic fluid

Once an ovum has been fertilized, it will develop into an embryo which will implant into the uterus. It is at this point that the amnion membrane forms. This is full of amniotic fluid and surrounds the embryo, protecting it against any knocks and bumps :)

3.10 describe the role of the placenta in the nutrition of the developing embryo

When an ovum is fertilized, it develops into an embryo and implants into the uterus. Once the embryo has implanted a placenta will develop. This lets the blood of the mother and baby get very close (BUT NOT TOUCH!) to allow the exchange of food, oxygen and waste.

NOTE: the blood of ma and ba to not touch. this is because they may have different blood types.

3.9 understand the role of oestrogen and progesterone in the menstrual cycle

Oestrogen causes the lining of the uterus to thicken and grow. It also stimulates the release of an ovum (well, it stimulates the release of LH which stimulates the release of an ovum).

Progesterone maintains the lining of the uterus. The lining breaks down when the level of progesterone falls.

2.90 understand the sources, roles and effects of the following hormones: ADH, adrenaline, insulin, testosterone, progesterone and oestrogen

ADH
Source: Pituitary gland
Role(s): ADH controls water content
Effect(s): Increases/decreases the permeability of the kidney tubules (in the nephrons) to allow more/less water to be reabsorbed into the bloodstream

Adrenaline
Source: Adrenal gland
Role(s): Hypes your body up, makes you ready for action
Effect(s): Increases your heart rate, increasing your blood flow to muscles (as faster heart rate means blood is pumped quicker) and increases your blood sugar levels

Insulin
Source: Pancreas
Role(s): helps to control blood sugar levels
Effect(s): Stimulates the liver to turn glucose into glycogen for storage

Testosterone
Source: Testes
Role(s): Testosterone is the main male sex hormone
Effect(s): Promotes male secondary sexual characteristics (post 3.12)

Progesterone
Source: Ovaries
Role(s): helps in pregnancy
Effect(s): maintains the lining of the uterus (so the fertilised egg can implant itself there)

Oestrogen
Source: Ovaries
Role(s): oestrogen is the main female sex hormone
Effect(s): Controls the menstrual cycle, promotes female secondary sexual characteristics (post 3.12)

2.89 describe the role of the skin in temperature regulation, with reference to sweating, vasoconstriction and vasodilation

When you are cold (and need to warm up)
- Blood vessels near the surface of the skin constrict (tighten) so that less heat can be transferred from the blood to the surroundings (this is vasoconstriction)
- You shiver to generate heat in your muscles (exercise will do the same thing, you just heat up)
- Very little sweat is produced (as sweat can cool you down)
- Hairs (on your arms, for example) stand on end (perpendicular to your skin) to trap a layer of air which will act as an insulator to keep you warm

When you are too hot (and need to cool down)
- Blood vessels near the surface of the skin dilate (widen) so that more blood can flow near the surface, allowing for more heat to radiate into the surroundings (this is vasodilation)
- You produce lots of sweat as, when it evaporates, it transfers heat from your skin to your surroundings (this cools you down)
- Your hairs lie flat to avoid any insulating layers of air being trapped

2.88 understand the function of the eye in focusing nearing distant objects, and in responding to changes in light intensity

By changing the shape of the lens the eye can focus on things near/far (this is known as accommodation). By changing the shape of the pupil the eye can adjust to different lighting intensities (e.g. see in bright light as well dim light).

Near objects
The ciliary muscle will contract (slackening the suspensory ligaments), this makes the lens appear more 'fat' (basically, its a little more curved).

Distant objects
The ciliary muscles relax and the suspensory ligaments contract, this makes the lens flatter

Light intensity
Bright light - triggers a reflex that makes the circular muscles contract causing radial muscles to relax, making the pupil smaller (allowing less light to enter so you don't get blinded). Light receptors detect bright light and send a message along a sensory neurone to an unconscious part of the brain, the message is passed onto a relay neurone that relays the message to a motor neurone which tells the circular muscle (the effector) in the iris to contract.

Dim light - this triggers a reflex that makes the radial muscles contract and circular muscles relax, this makes the pupil bigger allowing more light to enter. This works as light receptors detect a dim light and send a message to the sensory neurone to an unconscious part of the brain, this message is then passed to a relay neurone which relays it to a motor neurone which tells the redial muscles (the effector) to contract.

image source: midlandstech.edu

2.87 describe the structure and function of the eye as a receptor

The eye detects when light is strong/little and enlarges/shrinks the pupil when necessary (shrinking in bright light and enlarging in dim light)

Conjunctiva - this lubricates and protects the surface of the eye
Cornea - bends (refracts) light into the eye (it is transparent and has no blood vessels supplying it with oxygen so oxygen diffuses in from the outer surface)
Iris - this controls the diameter of the pupil, therefore it controls how much light enters the eye (big pupil = lots of light, little pupil = little light)
Lens - focuses the light onto the retina
Retina - the light-sensitive part of the eye. It is covered with  light receptors known as rods and cones (rods are more sensitive in dim light but cannot see colour, cones are sensitive to colours but are not very good in dim light, cones are found all over the retina but mostly at the fovea)
Optic nerve - this carries impulses to the brain

image credit: BBC

notes credit: CGP

2.86 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object.

- the pain receptor is stimulated by the hot pan - electrical impulses travel along the sensory neurone to the central nervous system - in the central nervous system the electrical impulses are passed onto a relay neurone - relay neurones pass the message to a motor neurone (via a synapse) - the electrical impulse will then travel from the motor neurone to the muscle - the muscle contracts and your hand moves away from the hot pan NOTE: the gap inbetween neurones is known as the 'synapse' and messages are passed across these synapses using chemicals Photo credit: Xth notes

2.85 understand that stimulation of receptors in the sense organs send electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses

When receptor in a sense organ detect a stimulus, electrical impulses are sent along sensory neurones (nerves) to the central nervous system (either to your spinal chord or an unconscious part of the brain). In the central nervous system, the sensory neurone passes the message onto the relay neurone - the gap between is called a synapse (the message is passed across the synapse with the help of chemicals). Next, relay neurones pass the message on to a motor neurone. The message will pass from a motor neurone to the effector. Lastly, the effector reacts (for example, a muscle will contract). This happens super duper quickly as they are automatic responses as you don't think about them (as they do not pass through the conscious part of your brain).

In other words, this is the reflex arc...

2.84 understand that the central nervous system consists of the brain and spinal chord and is linked to sense organs by nerves

The nervous system is made of all of the neurones in your body (including sensory, relay and motor neurones). However, the central nervous system consists of only the brain and the spinal chord. The central nervous system (CNS) is linked to sense organs (eyes, skin, nose, tongue, ears) by sensory neurones (these are nerves).

2.76 understand that urine contains water, urea and salts

In the beginning of the ultrafiltration/reabsorption process water, urea, salts and glucose are 'squeezed' our of the blood due to high pressure. However, during reabsorption all of the glucose (and a little bit of water and salts) is reabsorbed. Everything that remains in the glomerulus filtrate (water, urea and salts) is combined to form urine.

2.75 describe the role of ADH in regulating the water content of the blood

Osmoregulation determines how much water is reabsorbed into the blood at nephrons. The amount of water reabsorbed is controlled by ADH (anti-diuretic hormone). ADH makes the nephrons more/less permeable to allow more/less water to be reabsorbed back into the blood. This occurs like this...

- The brain is constantly monitoring the level of water in the blood
- The brain instructs the pituitary gland to release ADH into the blood (according to how much water needs to be reabsorbed)

NOTE: the process of osmoregulation is controlled by a mechanism called 'negative feedback'. This basically means if the water gets too high/low a mechanism will be triggered that brings the level down/up (back to normal)

2.74 understand that selective reabsorption of glucose occurs at the proximal convoluted tubule

ONLY glucose is absorbed at the first (proximal) convoluted tubule, this makes for selective reabsorption as only a certain substance(s) (in this case, glucose) can be absorbed, not everything is absorbed.

2.73 understand that water is reabsorbed into the blood from the collecting duct

If you don't know what happens regarding the water leaving the blood, it may be a good idea to go to one of these posts... 2.69 2.71 2.72. If you don't know what a nephron is or how it works, i would recommend checking out 2.71.

The glomerulus filtrate will flow along the nephron (next to the capillary). All the useful stuff (such as the glucose, some of the salt, and some of the water (depending on osmoregulation) will be reabsorbed (by active transport) back into the blood. The glucose is reabsorbed at the first (proximal) collecting tubule, the water is reabsorbed from the collecting duct, sufficient salt is kind of just absorbed throughout.

2.72 describe ultrafiltration in the Bowman's capsule and the composition of the glomerular filtrate

I have kind of answered this in 2.69 and 2.71 but here it is again just for bants

The renal artery will take oxygenated blood from the heart into the glomerulus (this is part of a nephron, in a kidney, go to 2.71 if you are unsure what a nephron is/how it work). This blood will build up in pressure as it is 'squashed' up. Due to the high pressure, all small molecules (such as glucose, water, urea and salts) will pass through a membrane inbetween the glomerulus and the Bowman's capsule, (all the bigger molecules will stay in the blood). The filtered liquid (the small molecules, e.g. water, glucose, urea and salts) is known as the glomerular filtrate.

2.71 describe the structure of a nephron, to include Bowman's capsule and glomerulus, convoluted tubules, loop of Henlé and collecting duct

Each of your two kidneys contains thousands of nephrons to help with osmoregulation and removal of urea (basically, they filter the blood). This is what they look like...

Inbetween the glomerulus and bowman capsule is a membrane that allows small molecules (such as water, glucose, urea and salts) to travel through, this is known as the filtrate and travels along through the orangey tube. As it travels, useful substances (such as glucose, some salt and a certain amount of water (depending on osmoregulation)) will be reabsorbed into the bloodstream (the red tube). All the unwanted stuff (like

urea, water and salt) is collected at the collecting duct. Here it all combines together to make urine which travels down the ureter, into the bladder where it is stored.

image credit: BBC

2.70 describe the structure of the urinary system, including the kidneys, ureters, bladder and urethra

Lets start with a diagram...

- The aorta takes oxygenated blood to the kidney (as the renal artery) and the vena cava takes deoxygenated blood away from the kidney (as the renal vein)

- The kidney is where the urea is turned into urine, there the blood is filtered (and the waste parts are taken out) and where osmoregulation occurs

- The urine travels down the ureter into the bladder

- Urine is stored in the bladder

- The urine travels down the urethra and out of the body

2.69 understand how the kidney carries out its roles of excretion and osmoregulation

Excretion
The kidneys remove urea from the blood. This is done in the nephron....

- Blood (from the renal artery) flows through the glomerulus, increasing pressure as it 'bunches up'.
- This high pressure causes small molecules (water, urea, glucose and salts) too squeeze through the membrane in-between the blood vessels (in the glomerulus) and the Bowman's capsule.
- This membrane acts as a filter so the bigger molecules (proteins and blood cells) do not leave the blood.
- As the filtrate (the small molecules that have been filtered out) flows through the nephron, the useful stuff (such as glucose) is selectively reabsorbed back into the bloodstream.
- The remaining substances are waste as they are of no use to the body, these substances include water, salts and urea.
- These remaining substances combine to form urine, which flows out of the nephron, through the ureter and down to the bladder where it is stored.

Osmoregulation
Osmoregulation is the adjustment of water content of the blood (it is a form of homeostasis). Basically, the kidney makes sure the blood has the right level of water in it. To do this, it has to constantly balance the amount of water that enters and leaves the blood. This is done by adjusting the amount of water the blood reabsorbed when flowing through the nephron. If the person is dehydrates (or very sweaty) the kidneys will reabsorb lots of water (this means less water is lost in urine). Similarly, if someone is very hydrated, the kidney can lower the level of water reabsorbed into the bloodstream, this means the person will lose more water through urine (this is why you wee loads if you drink loads). This is controlled by ADH (produced in the pituitary gland) which changes the permeability of the kidney tubules accordingly (to allow more/less water to be reabsorbed).

There is a little more on how osmoregulation takes place in post 2.75

2.68 recall that the lungs, kidneys and skin are organs of excretion

Excretion (removal of waste products) is carried out by the skin, the lungs and the kidneys.

The skin excretes waste salt etc as sweat (perspiration), the lungs excrete carbon dioxide, the kidneys excrete urea (urea is produces from excess amino acid in the liver).