Chapter 11: Excretion

Excretion – Process by which toxic materials and metabolic wastes are removed from the body of an

organism. Egestion – removal of undigested material from the alimentary canal = NOT EXCRETION.

Accumulation of nitrogenous and other compounds in an organism is harmful to the organism.

Excretory organs – Skin, kidney and lungs

URINE FORMATION

1. Ultrafiltration – mechanical filtration of different solutes (waste, nutrients) in the blood plasma,

except red and white blood cells that takes place due to a high hydrostatic blood pressure

produced by the difference in diameter between the afferent and efferent arteriole, in each

glomerulus, through a selectively permeable membrane.

For ultrafiltration to occur, there must be a high hydrostatic blood pressure formed because the

afferent arteriole has a larger diameter than the efferent arteriole. A partially permeable

membrane (aka. basement membrane) must be present as it acts as a filter and only allows small

molecules to pass through.

2. Selective reabsorption – process whereby useful materials are taken back into the blood stream

by osmosis (water), diffusion and active transport (glucose, amino acids)

Region Processes

First convoluted tubule

- Most of the mineral salts and all of the

glucose and amino acids reabsorbed by

diffusion and active transport.

- Most of the water is reabsorbed by osmosis.

Loop of Henle

- Remaining water is reabsorbed by osmosis.

Second convoluted tubule

- Remaining water is reabsorbed by osmosis.

- Mineral salts (eg. Na+) is reabsorbed by

diffusion and active transport.

Collecting duct

- Remaining water is reabsorbed by osmosis.

Excess water, excess salts and metabolic waste products (eg. urea, uric acid and creatinine)

pass out of the collecting duct into renal pelvis as a mixture called urine.

OSMOREGULATION WITH ANTI-DIURETIC HORMONE (ADH)

Dialysis

1. Kidney failure is fatal as the body is not able to remove waste materials such as urea and

other toxic chemicals.

2. Patients suffering from kidney failure can use a kidney dialysis machine to remove urea as

well as balance their salt concentration.

3. Blood is drawn from an artery in the patient’s arm and flows through a narrow tubing

throught the dialysis machine and is soon returned to a vein in the patient’s arm.

Characteristic of dialysis How it helps?

Partially permeable

tubing

Allows only small solutes such as urea, excess salts and

water to diffuse out from the blood while RBCs and

WBCs remain in the blood.

Long, narrow and coiled

tubing

Increases surface area to volume ratio to increase the

rate of diffusion.

Same concentration of

essential substances as

normal blood plasma

Ensures that these substances do not diffuse into the

dialysis fluid when the blood plasma has a higher

concentration of these substances.

Allows these substances to diffuse into the blood when

the blood plasma has a lower concentration of these

substances.

No metabolic waste in

supplied dialysis fluid

Ensures a steep concentration gradient which increases

the rate of diffusion of waste products to be diffused

out into the dialysis fluid.

Direction of blood flow is

opposite to direction of

flow of dialysis fluid

Maintains the concentration gradient at all sections of

the dialysis machine to increase rate of diffusion.

Treatment is 2-3 times a

week for a few hours

Allows sufficient time for the waste products to be

removed from the blood.

Chapter 12: Homeostasis

Homeostasis is the maintenance of a constant internal environment.

4 basic principles of homeostasis:

1. Stimulus – change in the internal environment

2. Receptor – detects the stimulus

3. Corrective mechanism – reverses effects of stimulus

4. Negative feedback – provides information to receptor to stop corrective mechanis,

Structure of mammalian skin

REGULATING HEAT IN THE BODY

Chapter 13: Nervous System

1. Central nervous system (CNS) consists of brain and spinal cord, Peripheral nervous system

(PNS) consists of cranial nerves and spinal nerves.

2. CNS does not come in direct contact with external environment. PNS comes in direct contact

with external environment.

Neurone part Form and function

Cell body

Contains nucleus and much of cytoplasm; most

of the metabolic activity of the cell occurs here

Axon

Transmits impulses away from the cell body

Dendrons

Transmits impulses towards the cell body

Dendrites

Terminal branches on axons and dendrons

Myelin sheath

Layer of fatty substance that encloses the nerve

fibre and insulates axon

Neurilemma

Thin membrane surrounding myelin sheath

Motor end plate (applicable to motor neuron)

Junction between dendrite and muscle fibre

Nodes of Ranvier

Regions where myelin sheath is absent allow

nerve impulses to jump from node to node,

increasing the speed of nerve transmission

direction of nerve impulse

direction of nerve impulse

Path of a nerve impulse

STIMULUS causes RECEPTOR to create impulse…

Step 1: Sensory neuron at receptor

Step 2: Sensory neurons in nerves

Step 3: Sensory neuron at dorsal root ganglion

Step 4: SAME sensory neuron in dorsal root

Step 5: SYNAPSE with relay neuron in grey matter in spinal cord (neurotransmitters released)

Step 6: Brain (processes information)

Step 7: Relay neuron in grey matter in spinal cord

Step 8: Motor neuron in ventral root

Step 9: Motor neuron in nerves

Step 10: Effector…

EFFECTOR causes RESPONSE

3. The nervous system serves to coordinate and regulate bodily functions.

4. A reflex is an immediate response to a specific stimulus without conscious control.

5. A reflex arc is the shortest pathway by which nerve impulses travel from the receptor to the

effector in a reflex action.

6. Receptors and effectors –

i. Knee jerk reflex: Sensory receptor in patellar tendon, Upper thigh muscle

ii. Hand on hot object reflex: Thermoreceptors in skin, Biceps

Chapter 14: The Human Eye

External eye part Form and function

Cornea

Frontal transparent dome-shaped part of the

eye. Refracts most of the light, providing most

of the eye’s focusing power.

Conjunctiva

Thin transparent epidermal layer that covers

anterior surface of the eye.

Iris

Coloured part of eye controls the light levels

inside the eye. Embedded with tiny muscles

that dilate and constrict the pupil size.

Pupil

Round opening in the centre of eye.

Eyelid

Protects the cornea from mechanical damage,

can be partly closed (aka. squinting) which

prevents excessive light from entering the eye.

Blinking spreads tears and wipes the dust

particles off the cornea.

Eyelashes

Helps shield eye from dust particles.

Tear gland

Secretes tears which washes dust particles

away, keeps cornea moist for atm oxygen to

dissolve and diffuse and lubricates conjunctiva

to reduce friction during blinking.

Sclera

Tough, white outer covering of the ball,

continuous with cornea, protects from

mechanical damage.

Choroid

Contains blood vessels that nourish the eye

tissue, pigmented black to prevent internal

reflection, connected to ciliary body and edges

of optic nerve, it is between sclera and retina.

Retina

Innermost layer of eye which contains

photoreceptors (ie. rods and cones) which

receive light and converts it into nerve

impulses that travel along optic nerve.

Lens

A transparent, circular and biconvex structure

which is elastic and changes its shape and

thickness to refract light into retina.

Suspensory ligaments

A tissue attaching the edge of the lens to the

ciliary body.

Ciliary body

A thickened region at the front end of the

choroid which contains ciliary muscles that

control curvature or thickness of lens.

Aqueous chamber

Space between lens and cornea, filled with

aqueous humor, a transparent, watery fluid that

keeps the front of the eyeball firm and helps to

refract light into the pupil.

Vitreous chamber

Space behind the lens, filled with vitreous

humor, a transparent, jelly-like substance that

keeps eyeball firm and helps refract light onto

the retina.

Fovea

Small yellow depression in the retina which is

situated directly behind the lens. This is where

images are normally focused. It has the greatest

concentration of cones but has no rods. This

allows detailed colour vision in bright light.

Optic nerve

A nerve that transmits nerve impulses to the

brain when the photoreceptors in the retina is

stimulated.

Blind spot

The region where the optic nerve leaves the

eye. It does not contain any rods or nerves

hence it is not sensitive to light.

Rods

Allow us to see in dim light, but only in black

and white as they contain visual purple,

formation of visual purple needs Vit A, more

sensitive to light than cones.

Cones

Allow us to see colours in bright light, three

types of cones: red, blue and green, each cone

contains a different pigment that absorbs light

of different wavelengths, do not work well in

dim light.

PUPIL REFLEX

Accommodation/ Focusing

1. Focusing on a distant object (ie. more than 7 metres)

STEP 1: Ciliary muscles relax, pulling on suspensory ligaments. (Chicken rice plates)

STEP 2: Suspensory ligaments become taut, pulling on edge of lens.

STEP 3: Lens becomes thinner and less convex, increasing its focal length.

STEP 4: Light rays from the distant object are sharply focused on the retina

STEP 5: Photoreceptors in the retina are stimulated.

STEP 6: Nerve impulses produced are transmitted by the optic nerve to the brain.

2. Focusing on a near object (ie. less than 7 metres)

STEP 1: Ciliary muscles contract, relaxes pull on suspensory ligaments. (Cheesy chicken rice)

STEP 2: Suspensory ligaments slacken, relaxing pull on edge of lens.

STEP 3: Lens becomes thicker and more convex, decreasing its focal length.

STEP 4: Light rays from the near object are sharply focused on the retina

STEP 5: Photoreceptors in the retina are stimulated.

STEP 6: Nerve impulses produced are transmitted by the optic nerve to the brain.

Chapter 15: Hormones

A hormone is a chemical substance, produced by a gland, carried by the blood, which alters the activity

of one or more specific target organs and is then broken down by the liver.

Exocrine glands pour their secretions out of the body via ducts or tube.

(eg. salivary gland, sweat gland)

Endocrine glands secrete their hormones into the bloodstream, has no ducts or tube.

(eg. pituitary gland, adrenal gland)

Pancreas is an exocrine and an endocrine gland as:

1. Secretes pancreatic juice carried away by pancreatic duct to duodenum.

2. Islets of Langerhans secrete insulin and glucagon (hormones) into bloodstream

Endocrine glands:

Pituitary gland (ADH as well as master gland), hypothalamus (regulates secretion of some pituitary

hormones), thyroid gland (thyroxine), ovaries (progesterone and oestrogen), testes (testosterone),

adrenal gland (adrenaline), pancreas (insulin and glucagon)

Hormone Effects

Adrenaline

1. Increases blood glucose level by speeding up

breakdown of glycogen to glucose which is then

transported to the heart and skeletal muscles.

2. Increases metabolic rate and increases energy

released in tissue respiration.

3. Increases rate of heartbeat and causes a rise in

blood pressure so that oxygen and glucose are

transported faster to the muscles.

4. Increases the rate and depth of ventilation.

5. Constricts arterioles in skin causing paleness,

thus channeling more blood to muscles.

6. Increases rate of blood coagulation.

7. Causes pupil to dilate to enhance vision.

8. Contracts hair muscles, producing ‘goose

bumps’.

Insulin

Lack:

1. Diabetes mellitus

(refer to later part of notes)

2. Body becomes weak and continously loses

weight as muscle cells have no store of

glycogen.

3. Oxidises fats into ketones to produce

energy, ketones removed in urine.

Insulin

Normal:

Decreases blood glucose concentration by:

i. increasing permeability of cells to

take up glucose

ii. stimulating liver and muscle cells

to convert glucose to glycogen

iii. increase oxidation of glucose in

tissue respiration

Over:

Abnormal decrease in blood glucose concentration.

Shock, coma and death may follow.

Glucagon

Increases blood glucose level by

i. Converting glycogen to glucose

ii. Converting fats and amino acids to

glucose

iii. Converting lactic acid to glucose

REGULATION OF BLOOD GLUCOSE LEVELS

Type 1 diabetes Type 2 diabetes

Other names

Juvenile, early-onset diabetes

Late-onset diabetes

Signs

Persistently high blood glucose level, presence of glucose in urine,

slow healing of wounds.

Treatment

Insulin injections, diet of sugary

foods (eg. glucose sweets)

Insulin injections, regulation of

carbohydrates, metformin tablets,

exercise.

Nervous system Hormonal system

Involve nerve impulses (electrical signals) Involves hormones (chemical substances)

Impulses transmitted by neurons Hormones transported in blood

Usually quick responses Usually slow responses

Responses are short-lived Responses may be short- or long-lived

May be voluntary or involuntary Always involuntary

Usually localised Tend to affect more than one target organ