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.
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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)