Exams Flashcards
Exocrine glands
− Secrete into a duct that carries the secretion to the body surface or body cavity
e.g. sweat glands, mucous glands, salivary glands and glands of alimentary canal
Endocrine glands
− Secrete hormones into the extracellular fluid that surrounds the cells that make up a gland
− Transported by the blood
Hormones
− A chemical that is secreted by an endocrine gland and that affects the functioning of a cell or organ; often carried in blood
− May be proteins, steroids or amines
− Only affects particular groups of cells or organs, called target cells and target organs
− Hormones can only influence cells with the correct receptors
− Once all receptors are occupied, the addition of more hormones does not produce any greater effect
Hormones may…
− Activate certain genes in the nucleus so that a particular enzyme or structural protein is produced
− Change the shape or structure of an enzyme so that it is turned ‘on’ or ‘off’
− Change the rate of production of an enzyme or structural protein by changing the rate of transcription or translation during protein production
Paracrines
Any chemical secreted by a cell that diffuses to and affects adjacent cells; also called local hormone. They are secreted by all cells.
Protein & Amine hormones
Work by attaching to receptor proteins in the membrane of the target cell. Causes the 2nd messenger to diffuse and activate enzymes.
Steroid Hormones
Work by entering target cells and combining with a receptor. The hormone-receptor complex activates the genes controlling the formation of proteins
Enzyme Amplification
− A series of chemical reactions in which the product of one step is an enzyme that produces an even greater number of product molecules at the next step
− A very small stimulus can produce a very large effect
Hormone Clearance
− Hormone must be turned ‘off’
− Hormone molecules get broken down
− Broken down in target cells, but most in the liver and kidneys
− Degraded hormones are the exerted either in the bile or in the urine
Control of hormone secretion
− Maintain homeostasis, amount of hormone produced has to be closely regulated
− Over or under secrete will cause body to function abnormally
− Regulated by negative feedback
− The hypothalamus can secrete releasing factors, which stimulate the release of a hormone, or inhibiting factors, which slow down the secretion of a hormone
The hypothalamus
− Located at the base of the brain
− Regulates many basic functions
e.g. body temp, water balance and heart rate
− Function are carried out through the pituitary gland
− Produces many different hormones
− Some carried in the blood to anterior lobe, where they stimulate or inhibit the release of hormones
− Other hormones pass along the nerve fibres from hypothalamus to the posterior lobe, where they are secreted
Pituitary Gland
− Lies under the hypothalamus
− No bigger than a large pea, approx 13 mm in diameter
− Anterior and posterior lobes
− Anterior, no nerves connecting to hypothalamus - complex network of blood vessels
− Posterior doesn’t secrete substances, connected by nerve fibres
Anterior Lobe
Secretions of the anterior lobe are controlled by releasing and inhibiting factors secreted by the hypothalamus, secreted in the extracellular fluid around cells of the hypothalamus and carried by blood to anterior lobe
Posterior Lobe
− Hormones not manufactured here
− Produced in spinal nerve cells in the hypothalamus of the brain
− Cells have long extensions that pass through infundibulum to posterior lobe
− Hormones move down extensions and stored ready for release into bloodstream
− Release of hormone triggered by nerve impulses
ANT PIT
FSH
Ovaries; growth of follicles
Testes; production of sperm
ANT PIT
LH
Ovaries; ovulation and maintenance of corpus luteum
Testes; Secretion of testosterone
ANT PIT
GH
All cells; growth and protein synthesis
ANT PIT
TSH
Thyroid gland; secretion of hormones from the thyroid
ANT PIT
ACTH
Adrenal cortex; secretion of hormones from the adrenal cortex
ANT PIT
PRL
Mammary glands; milk production
POST PIT
ADH
Kidneys; reabsorption of water
POST PIT
OT
Uterus; contractions of uterus during childbirth
Mammary glands; release of milk
The pineal gland
A small gland, about the size of a pea in children, found deep inside the brain; in adults it is just a lump of fibrous tissue; the functions of the hormones it secretes have still not been identified.
− Known to secrete melatonin, which is involved in regulation of sleep patterns and stimulated by darkness
The thyroid gland
An endocrine gland, consisting of 2 lobes, located in the neck just below the larynx, secretes the hormone thyroxine.
− Thyroxine controls body metabolism
− Brings about the release of energy and to maintain body temperature
− Secreted in response to TSH
The parathyroid gland
One of four (usually) small glands about the size of a small pea embedded in the rear surface of the thyroid gland; secretes PTH which control calcium and Phosphate levels in blood.
The thymus
An endocrine gland located in the chest just above the heart and behind the sternum; secretes a group of hormones called thymosins. these hormones influence the maturation of disease-fighting cells called T lymphocytes.
The adrenal glands
− 2, one above each kidney
− Each has an inner adrenal medulla and an outer adrenal cortex
Adrenal Medulla
The inner portion of an adrenal gland; secretes the hormones adrenaline and noradrenaline
− Adrenaline (epinephrine) prepares the body for the fight or flight responses; also acts as a neurotransmitter by transferring nervous impulses across the junction (synapse) between adjacent nerve cells
− Noradrenaline (norepinephrine) has effects similar to adrenaline; in particular it increases the rate and force of the heart beat
Adrenal cortex
More than 20 different hormones are produced in the adrenal cortex and they are known collectively as corticosteroids. the 2 main ones are:
− Aldosterone, which acts on the kidney to reduce the amount of sodium and increase the amount of potassium in the urine
− Cortisol, which, with related hormones promotes normal metabolism, helping the body to withstand stress, and also helps with repair of damaged tissues
The pancreas
A gland that lies just below the stomach; both an endocrine and exocrine gland; that secretes digestive enzymes from the exocrine glands, and the hormones insulin and glucagon from a cluster of special cells called Islets of Langerhans, which are part of the endocrine part of the pancreas.
− Insulin, reduces the amount of glucose in the blood, the blood sugar level. Promotes the uptake of glucose from the blood by cells. The level of secretion is determined by the amount of sugar in the blood and controlled through a negative feedback system
− Glucagon, increases the blood sugar level
The gonads
− Androgens, are the male sex hormones produced by the testes. Responsible for the development and maintenance of the male sex characteristics
− Oestrogen and progesterone ate the female sex hormones produced by the ovaries. Stimulate the development and maintenance of the female sexual characteristics
Other Endocrine Tissues
There are other tissues, many of which are not called endocrine glands, that secrete hormones.
− Stomach and small intestines, both secrete hormones that coordinate the exocrine glands of the digestive system
− Kidneys, secrete hormones including erythropoietin (EPO), stimulates production of red blood cells by the bone marrow
− Heart, secretes hormone that helps reduce blood pressure
− Placenta, secretes many hormones during pregnancy that help to maintain the pregnancy and stimulate the mother’s mammary glands
Nervous System
The body system involved with control and coordination of the body
Central Nervous System
The part of the nervous system that consists of the brain and spinal cord
Peripheral Nervous System
The part of the nervous system that connects the CNS with the receptors, muscles and glands
Neurons
− Neuron, a nerve cell; the basic structural and functional unit of NS
− Vary in shape and size, but all consist of a cell body and 2 extensions form the cell; the dendrites and the axon
− Most neurons are Interneurons, they have many branches that are able to send or receive messages to or from adjacent neurons
− The cell body is part of the neuron that contains the nucleus
− Dendrites, an extension of the body of a nerve cell; carries nerve impulses into the cell body
− Axon, an extension of the body of a nerve cell, carries nerve impulses away from the cell body
− Axon length varies, short in brain and up to a metre long from spinal cord to foot
− Most axons covered with a layer of fatty material call the myelin sheath
− Nerve fibres (axon) with myelin sheath call myelinated fibres and those without are called unmyelinated fibres
− White matter consists of nerve cell bodies and unmyelinated fibres
− Grey matter consists of nerve cell bodies and myelinated fibres
− Outside the brain and spinal cord the myelin sheath is formed by special cells called Schwann cells, which wrap around the axon
− At intervals along the axon are gaps in the myelin sheath, called nodes of Ranvier
− Sheaths 3 main functions; acts as an insulator, protects axon form damage and speed up the movement of nerve impulses along the axon
− Neurilemma, a sheath surrounding a nerve fibre; helps in the repair of injured fibres
Sensory (receptor) neurons
carry messages form receptors in the sense organs (or skin) to CNS
Motor (effector neurons)
carry messages from CNS to muscles and glands (effectors)
Interneurons
are located in CNS and link sensory and motor neurons
Multipolar neurons
one axon and multiple dendrites
Bipolar neurons
one axon and one dendrite. Occur in the eye, ear and nose
Unipolar neurons
just one axon. Most sensory neurons
Synapses
The junction between the branches of adjacent neurons.
− At synapse neurons don’t actually join, small gap
− Messages have to be carried across the synapse
− Neuromuscular junction, where an axon meets a skeletal muscle cell
Nerve Impulses
The electrochemical charge that travels along the membrane of a nerve cell; the message carried by a nerve. Transmitted very quick, makes it possible for the body to respond rapidly to any change.
− The speed at which an impulse travels depends on whether the nerve fibre is myelinated or unmyelinated
− Unmyelinated, the impulse travels steadily (max speed 7km/h)
− Myelinated, the myelin sheath is not continuous. Gaps called nodes of Ravier. Impulse jumps from node to node
− This jumping is known as saltatory conduction, allows faster travel
Divisions of NS
− CNS and PNS
− PNS consists nerve fibres, carry info to and from the CNS and groups of cell bodies called ganglia (lie outside the brain and spinal cord)
− 12 pairs of nervous arise from the brain, these are the cranial nerves
− Most cranial nerves are mixed nerves, carry impulses to and away from brain
− Fibres that carry impulses into the CNS are called sensory fibres
− Motor fibres, carry impulses away from CNS
− 31 pairs of spinal nerves arise from spinal cord
− They all mixed nerves and joined to spinal cord by 2 roots
− Ventral root contains axons of motor neurons (grey matter)
− Dorsal root, axons of sensory neurons (cell bodies in small swelling on the dorsal root, dorsal root ganglion)
Afferent (sensory) Division
− Carry impulses into the CNS
− Carried by sensory nerve cells from receptors in the skin and around the muscles and joints
− Nerve cells called somatic sensory neurons
− Visceral sensory neurons take impulses from internal organs to CNS
Efferent (motor) Division
Has fibres that carry impulses away from the CNS. It is subdivided into:
− Somatic Division - takes impulses from CNS to the skeletal muscles
− Autonomic Division - Carries impulses from CNS to heart muscle, involuntary muscle and glands (further divided into sympathetic and parasympathetic division)
Autonomic Nervous System
− Part of PNS
− Responsible for control of body’s internal environment
e.g. heart rate, blood pressure, body temp, digestion, release of energy, pupil diameter, air flow to the lungs, defecation and urination
− Usually operates without conscious control and regulated by groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex
− 2 motor neurons involved in the autonomic pathway carry impulses from the CNS to the effector
− Most organs under autonomic control receive 2 sets of nerve fibres (sympathetic and parasympathetic fibres)
− Acetylcholine or noradrenaline carries the message to the effector
− Parasympathetic division generally produces responses that maintain the body during relatively quiet conditions
− Sympathetic division tends to produce responses that prepare the body for strenuous physical activity (fight or flight responses)
− Message form autonomic nerves to the muscle and glands under their control is carried by a neurotransmitter at the nerve endings
− Parasympathetic nerve endings release acetylcholine
− Sympathetic nerve endings release noradrenaline
Fight or flight
Fear, anger, stress, danger and competition provoke fight or flight responses. Activation of the sympathetic division results in the following responses:
− Increase blood pressure
− Blood vessels dilate (heart, liver and skeletal muscles)
− Blood vessels constrict (kidney, stomach, intestines and skin)
− Breathing increases
− Blood glucose levels rise
− Increase sweat
Comparison of hormonal and nervous coordination
Bothe the endocrine system and NS do not duplicate each other’s roles; rather, they complement and reinforce each other. The difference between the actions of nerves and hormones are as follows:
− Ns more rapid response (impulses travel rapidly along nerve fibres and hormone transported in the bloodstream)
− Nerve impulses immediate response, but hormones are slow-acting
− Nervous messages are an electrochemical charge and hormones are chemicals
− Nerve impulses specific target (effector), but hormones go everywhere and may affect a number of organs
Important similarities between the 2 systems:
− Hormones secreted by neurons into the extracellular fluid (OT and adrenaline)
− Function as both hormone and neurotransmitter (noradrenaline, ADH and dopamine)
− Some hormones and neurotransmitters have same effect on the same target cells
the protection of the cns
− Bone
− Membranes called meninges
− A fluid called cerebrospinal fluid (CSF) Outermost layer is bone (cranium)
− Spinal cord runs through vertebral canal (opening in the vertebrae)
− 3 layers of connective tissue cover surface of brain and spinal cord, called meninges
− Outer meninge layer, tough and fibrous
− Middle meningeal layer is loose mesh of fibres
− Inner layer is far more delicate, contains many blood vessels and sticks closely to the surface of the brain and spinal cord
− CSF occupies space between middle and inner layers of meninges
− CSF is clear, watery fluid containing a few cells and some glucose, protein, urea and salts
− Acts as a shock absorber
− Also supports brain
− Circulates and takes nutrients to cells of the brain and spinal cord and carries away their waste
− CSF; protection, support and transport
Structure of the cerebrum
− Biggest part of brain
− Outer surface of grey matter (2-4mm thick) known as cerebral cortex
− Below cortex is white matter
− Deep inside is additional grey matter, basal ganglia
− Cerebral cortex, folded patterns, increases SA
− Cortex contains 70% all neurons in CNS
− Folds create convolutions (or gyri), separated by shallow down folds called sulci or deep down folds called fissures
− Longitudinal fissure (deepest) almost separates the cerebrum into 2 halves, left and right cerebral hemispheres
− Corpus Callosum, a large bundle of nerve fibres that connects the 2 hemispheres, can’t be seen on the outside of the brain
− Certain fissures and sulci are fairly constant used to separate into 4 lobes - frontal, temporal, occipital and parietal lobes
− Insula, deep inside the brain regarded as 5th lobe
− Within CNS bundles of nerve fibres are called tracts (outside CNS called nerves)
− 3 types - connect various areas of cortex within the same hemisphere, carry impulses between left and right hemispheres and connects cortex to other parts of the brain or spinal cord
Functions of cerebrum
Cerebral cortex is involved in meta; activities such as; thinking, reasoning, learning, memory, intelligence and sense of responsibility. Also concerned with perception of the senses and the initiation and control of voluntary muscle contraction. There are 3 types of functional area in cortex:
− Sensory areas, which impulses form receptors (receives and processes nerve impulses form the senses)
− Motor areas, which control muscular movement (send impulses to muscles, especially for voluntary movement)
− Association areas, which are concerned with intellectual and emotional processes (interpret info form the sense and make it useful)
The Corpus Callosum
A wide band of nerve fibres that lies underneath the cerebrum at the base of the longitudinal fissure. Nerve fibres in the corpus callosum cross from one cerebral hemisphere to the other and allow the 2 sides of the cerebrum to communicate with each other
The Cerebellum
− Lies under the rear part of the cerebrum
− 2nd largest part of the brain
− Folded into a series of parallel ridges (surface)
− Outer, grey matter
− Inside, white matter
− Control over posture, balance and the fine coordination of voluntary muscle movement
− Receives sensory information from inner ear (for posture and balance) and from stretch receptors in the skeletal muscles
− All functions take place below the conscious level
− Without cerebellum could still move but would be spasmodic, jerky and uncontrolled
The hypothalamus
Lies in the middle of the brain and cannot be seen from the outside. Although small, the hypothalamus controls many body activities, mainly concerned with homeostasis (maintaining a constant environment for cells). Functions of the hypothalamus include regulation of:
− The autonomic NS
e.g. heart rate, blood pressure, the secretion of digestive juices, movements of the alimentary canal and the diameter of the pupil of the eye
− Body temp
− Patterns of walking and sleeping
− Contraction of urinary bladder
− Emotional responses
e.g. fear, anger, aggression, pleasure and contentment
− Secretion of hormones
The medulla oblongata
Continuation of the spinal cord. It is about 3cm long and extends from just above the point where the spinal cord enters the skull. The Medulla Oblongata contains:
− Cardiac centre, which regulates the rate and force of heartbeat
− Respiratory centre, which controls rate and depth of breathing
− Vasomotor centre, which regulates the diameter of blood vessels
There are others that regulate the reflexes of swallowing, sneezing, coughing and vomiting. All centre’s are influenced and controlled by higher centre’s in the brain, particularly the hypothalamus.
The spinal cord
− A roughly cylindrical structure that extends from the foramen magnum (the large opening at the base of the skull to the second lumbar vertebrae)
− About 44cm long
− Cord is enclosed in the vertebral canal (inside ring of bone, 3 meningeal layers)
− Outermost layer not connected to bone
− Space containing fat, connective tissue and blood vessels
− Serve as padding around spinal cord, allows the cord to be bent when the spine is bent
− Grey and white matter (grey centre)
− Grey matter roughly shape letter H
− Central canal, a hollow that runs through the centre of the spinal cord; filled with cerebrospinal fluid
− Ascending tracts are sensory axons that carry impulses upwards, towards the brain
− Descending tracts contain motor axons that conduct impulses downwards, away from brain
receptors
− Structure that is able to detect change in body’s internal or external environment (stimulus)
− Receptor cells of particular type grouped together in a sense organ
thermoreceptors
− Able to respond to heat and cool
− Located in the skin or the hypothalamus
osmoreceptors
− Receptors sensitive to osmotic pressure of body fluids
− Located hypothalamus
− Osmotic pressure determine by the concentration of substances in the water of the blood plasma
Chemoreceptors
− Sensitive to particular chemicals
e.g. present in nose and mouth
Touch receptors
− Receptor sensitive to touch
− Mainly found in skin
− receptors close to surface of skin are sensitive to very light touches
e.g. lips, fingertips and eyelids
− Receptors located deeper in the skin are sensitive to pressure and vibrations
Pain receptors
− Stimulated by damage to tissues
e.g. from a cut or a heavy bump, poor blood flow to a tissue, or by excessive stimulation from stimuli such as heat or chemicals
− Occur in most organs, not brain
− Pain is uncomfortable but essential
− Warns us of damage to tissues occurring
− Pain receptor adapt little or not at all
Reflexes
Is a rapid, automatic response to a change in the external or internal environment. All reflexes have four important properties: − Stimulus is required − Reflex is involuntary − Reflex response is rapid − Reflex response is stereotyped
− Most are coordinated by the spinal cord
− Spinal reflex, carried out by the spinal cord without involvement of the brain
− Reflex arc, the pathway travelled by nerve impulse form receptor to effector
− Spinal reflex, a spinal reflex arc pathway travelled by nerve impulses from receptor to effector
− Spinal reflex, involuntary (doesn’t involve brain)
Reflex arc
− A receptor, either the ending of a sensory neuron or a specialised cell associated with the end of a sensory neuron
− A sensory neuron, carries impulses form the receptor to CNS
− There is at least one synapse
− A motor neuron, carried the nerve impulse to an effector
− An effector, receives the nerve impulse and carries out appropriate response
components in a simple spinal reflex
- Pain receptors in the skin detect the stimulus and produce a nerve impulse
- Sensory neuron conducts the nerve impulse from the receptor to the spinal cord
- Information is processed in the CNS. 1 or more interneuron’s pass the message to the appropriate motor neuron
- Motor neuron carries a nerve impulse to the effector
- he effector, in this case the biceps muscle contracts, removing the hand form the painful stimulus
− Response occurs in fraction of a second
− Impulses would travel up the spinal cord to the brain
− After response, person becomes consciously aware
− Many reflexes protect body from injury
− Other reflexes secretion
Learned reflexes
− More complex motor patterns during a baby’s development
e.g. suckling, chewing or following movements with the eyes
− Determined genetically
− Acquired reflexes, a response to a stimulus that has been learned through practice
e.g. muscular adjustments whilst riding a bike, catching ball and jamming on brakes in car
Homeostasis
− The process of keeping the environment inside the body fairly constant
e.g. body temp, pH, oxygen and glucose levels and waste removal
− Equilibrium, input and output of materials and energy are balanced
− All systems of body contribute to homeostasis
− NS and endocrine system are the main sensory and controlling body systems, in the case of homeostasis
Aspects of internal environment that the body needs to regulate
− Core body temp
− pH concentration of dissolved substances in the body fluids
− Concentration glucose, oxygen and carbon dioxide in blood
− Blood pressure
− Concentration of metabolic wastes
Tolerance Limit
− Limits of factors such as temp and fluid balance beyond which the body malfunctions
− The upper and lower limits to a range of factors
− Within these limits the body functions normally
− Rise above, fall below the normal range means that the individuals tolerance limits have been exceeded and dysfunctions will occur
Feedback Systems
− Circular situation which the body responds to a change (stimulus), with response altering original stimulus
− Negative feedback system, a situation in which feedback brings about a change opposite to, or reduces the effect of, the original stimulus
Feedback systems include
− Stimulus, the change in environment that causes the system to operate
− Receptor, detects change
− Modulator, control centre responsible for processing info received from receptor and sending info to effector
− Effector, carries out a response counteracting the effect of the stimulus
− Feedback, achieved because original stimulus been changed by the response
Negative feedback
− Feedback that reduces the effect of , or eliminates, the original stimulus
e.g. feeling cold. Response, you put on a jumper and no longer feel cold. Response has reduced or eliminated the original stimulus of feeling cold
− Dynamic equilibrium, a state reached when the rates of forward and reverse changes are equal; a stable balanced or unchanging system results
e.g. concentration of blood glucose and body temp fluctuate around a normal level
− Set point, the level at which a variable is to be maintained
e.g. body temp of 37°C
positive feedback
− Feedback that reinforces the original stimulus
e.g. occurs during childbirth and blood clotting and high fever (dangerous)
− Positive feedback has no role in homeostasis
thermoregulation
The regulation of body temp; the balance of heat gain and heat loss in order to maintain a constant internal body temp independent of the environmental temp.
− Cells are very heat-sensitive
− Optimum 37°C
− Heat produced from metabolic activity helps to maintain this high level
− Increased body temp can cause nerve malfunction, change in the structure of proteins and death
− Lowest body temp usually occurring in the morning and highest in the evening
Heat production
− Most energy is released in the form of heat
− The rate at which energy is released by the breakdown of food is called metabolic rate
− During exercise metabolic rate is increased and large quantities of heat are released
temperature receptors
− Thermoreceptors
− Those in skin and in some mucous membranes are called peripheral thermoreceptors
− Others are located in the hypothalamus are called central thermoreceptors
− Peripheral receptors provide the hypothalamus with info about the external environment
− Hypothalamus is the body’s main temp-regulating centre
peripheral thermoreceptors
− Cold Receptors; a receptor stimulated by low temp
− Heat Receptors; a receptor stimulated by high temp
Skin and temperature regulation
− Changes in skin can speed up or slow down the rate at which heat is lost from the body
− Blood vessels carry hear to the skin from the core of the body
− Heat can then be lost from the skin by conduction, convection, radiation and evaporation
− Diameter of blood vessels to the skin controlled by autonomic nerves, can act to increase to decrease the flow of blood near the surface therefore increase or decrease the rate of heat loss
− These adjustments keep core body temp constant
− Body heat must be lost and skin blood vessels already at max dilation, sweating occurs
− Sweating is an active secretion of fluid by sweat glands
− Evaporation of swear form skin is a cooling process
− Cooling of skin results in the cooling of the blood flowing through the skin
Preventing body temp from falling
The body can respond by physiological changes and behavioral changes:
− Vasoconstriction; a decrease in the diameter of blood vessels, increasing the flow of blood. The skin becomes cooler as there is less warm blood flowing through, helps maintain body temp in cold conditions
− Stimulation of the adrenal medulla by sympathetic nerves. Results in the release of adrenaline and noradrenaline in the blood therefore increase in cellular metabolism which leads to increase in heat production. Helps maintain their rapid heat loss
− Shivering can increase body heat production
− Increase in production of thyroxine . Causes increase in metabolic rate resulting in body temp. Slower to have an effect
− Behavioural response; put on a jumper
Preventing body temp from rising
The following responses ensure that body temp does not rise:
− Vasodilatation; an increase in the diameter of blood vessels, increasing the flow of blood. The skin becomes reddish in colour, surface temp rises and there is greater heat loss through radiation and convection
− Sweating is needed for temps above approx. 28°C, to increase heat loss
− Decrease in metabolic rate, means less heat is produced
− Behavioural response; air conditioner or fan
Control of thermoregulation
Hypothalamus monitors the temp of blood and receives impulses from peripheral thermoreceptor
Temperature tolerance
− Core body temp over 42°C dangerous, death usually above 45°C
− Temp and relative humidity high, difficult to lose heat to radiation and evaporation
− Heat stroke is the failure of a person’s temp-regulating mechanisms when exposed to excessive heat
− Heat exhaustion is the collapse of a person after exposure to heat, during which their body’s heat-regulating mechanisms continue to function normally
− Extreme cold can also cause death, core temp drops below 33°C, metabolic rate is so low heat production can’t replace heat loss, body temp continues to fall, called hypothermia
body fluids
− Body approx. 60% water (45% - 75%)
− Males, average 65%
− Females, average 55%
− Water is contained in various body fluids
− Fluid inside cells called the intracellular fluid or cytosol
− Fluid outside cells is the extracellular fluid
− Extracellular fluid included the blood plasma and the fluid between the cells, called intercellular fluid (interstitial fluid and tissue fluid)
− Plasma separated form the intercellular fluid by thin walls of the capillaries, there is relatively free exchange of material between the 2
fluid balance
− Fluid gain must equal fluid loss
− Most body fluid obtained from water
− Small amount formed as a product of cellular resp
− Fluids are lost from the body via the kidneys, through the skin, from the surface of the lungs and from alimentary canal
− Typically, 2.5L lost each day
excretion
Removal of wastes of metabolism from the body. Many wastes are toxic, harmful if allowed to accumulate in the body fluids. Several organs in the body take part in excretion:
− Lungs excrete CO2
− Sweat glands in the skin secrete water containing by-products of metabolism such as salts, urea and lactic acid
− Alimentary canal passes out bile pigments that entered the small intestine with the bile. These pigments are the breakdown products of haemoglobin in RBC, they leave body with faeces
− Kidneys are the principal excretory organs. they are responsible for maintaining a constant concentration of materials in the body fluids
the kidneys
− Approx. 60% of water lost form body each day is excreted by the kidneys as urine
− only water loss from the kidneys can be regulated to achieve a constant concentration of dissolved substances in the body fluids
− Not just excretory organs, they play a major role in regulating the composition of body fluids
− Ureter; the tube that leaves each kidney and drains into the urinary bladder
− Urethra; the tube that empties the bladder to the outside
− Each kidney contains about 1.2 million nephrons
− Nephron; the functional unit of the kidney, carries out the kidney’s role in excretion and water regulation
control of water loss by the kidneys
- If a decreased amount of water is in the blood, such as would result from increased loss of water through sweat, the water concentration of the blood plasma would decrease. This means the osmotic pressure of the blood is raised.
- Osmoreceptors in the hypothalamus detect the increases osmotic pressure of the blood.
- The hypothalamus stimulates the posterior lob to release ADH into the bloodstream.
- ADH is carried all over the body by the blood but it affects target organs.
- More water is then reabsorbed into the blood plasma form the tubules and ducts.
- The reabsorption of water increases the water concentration in the plasma and so the osmotic pressure of the blood is decreased.
- The response is decreased osmotic pressure of the blood. This has eliminated or reduced the originals stimulus that was increasing osmotic pressure of the plasma. negative feedback has occurred.
− Aldosterone is another hormone that plays a part in the regulation of water output
− Secreted by adrenal gland
− Increased aldosterone secretion has the indirect effect of increasing blood pressure
regulating water intake
The events that take place to bring about intake of water and restoration of the water balance:
- As water is lost from the various body fluids, there is reduction in plasma volume and an increase in osmotic concentration of the extracellular fluid
- Osmosis receptors in a thirst center in the hypothalamus detect the rising osmotic concentration of the blood. Other stimuli such as a dry mouth are also involved.
- Stimulations of the thirst center makes the person feel thirsty.
- The conscious feeling of thirst stimulates the person to drink.
- The fluid consumed is absorbed into the plasma from the alimentary canal.
- As the blood circulates through the body, it enables the intercellular fluid and intracellular fluid to return to the proper osmotic concentrations.
- Drinking, the thirst center is no longer stimulated and the desire to take in water ceases. This is another negative feedback loop.
Too much/too little water
- Dehydration; excessive loss of water accompanying salts from the body, results when the body loses more fluid than it takes in.
- Symptoms include; serve thirst, low blood pressure, dizziness and headaches
- Water intoxication; a potential life threatening conduction caused by drinking too much water when the amount of salt (and other electrolytes) in the body is low; commonly caused by long bouts of intensive exercise during which electrolytes are not replenished and large amounts of water are consumed.
- First sign is usually lightheadedness
- Headaches, vomiting and collapsing may follow.
regulation of blood sugar
− Forms of glucose
− Glucose is source of energy
− Energy is released from glucose through cellular respiration
C6H12O6 + O2 → CO2 + H2O + energy
− Carbohydrates broken down into glucose during digestion
− Absorbed through walls of small intestine
− After meal, blood glucose concentration increase rapidly
− Homeostatic mechanisms begin to decrease blood glucose concentration and maintain normal level
− Excess must be stored, for future activity
− Glycogen; made of long chains of glucose, stored in liver and muscle cells
− Pancreas and adrenal glands secrete hormones to affect the level of glucose in blood
− Glycogen stored, can turn to glucose and be added to blood
role of the liver
− Able to convert glucose into glycogen or vice versa to release into blood
the hepatic portal vein carries the glucose to the liver where a number of things may occur
− Glucose may be removed from blood by liver to provide energy for liver functioning
− May be removed by liver/ or muscle and converted into glycogen for storage
− May continue to circulate in blood, for cells to absorb for energy
− Excess glucose (normal blood sugar and tissue glycogen) converted to fat
− Glycogenesis; the process whereby glucose molecules are chemically combined in log chains to form glycogen molecules
− Glycogenesis is stimulated by the pancreatic hormone insulin
− Glycogen has to be converted back to glucose to be usable
− Glycogenolysis; the process of converting glycogen back to glucose
− Frequently occurs between meal and is stimulated by another by another pancreatic hormone, glucagon
− Glycogen is short term energy supply
− After that is used the body uses the energy reserves in stored fat
role of the pancreas
− Within pancreas are clusters of hormone - secreting cells called the Islet of Langerhans
− Contains alpha cells, secrete glucagon and the beta cells, secrete insulin
− Insulin cause decrease in blood sugar levels
− It accelerate transport of glucose from the blood into the cells and also accelerates the conversion of glucose into glycogen
− Glucogen from the alpha cells cause increase in blood sugar levels
− Glycogenolysis is the conversion of glycogen to glucose, in the liver
− Glucose is then released into the blood and blood sugar rises
− Glucagon stimulates liver to produce new sugar molecules from fats and amino acid, process called Gluconeogenesis
role of the adrenal glands
− Outer part called the Cortex – stimulated by ATCH by anterior lobe
− Inner part called Medulla
− Secretion of glucocorticoids by the adrenal cortex - cortisol
− Adrenaline and noradrenaline secreted by adrenal medulla
− Cortisol regulates carbohydrates metabolism (making sure enough energy is provided to cells
− Stimulate conversion of glycogen to glucose
− increase rate that amino acids are removed form cells and transported to liver
− Some amino acids are converted to glucose, if glycogen and fat levels are low (gluconeogenesis)
− Adrenaline and noradrenaline stimulates breakdown of glycogen in liver and release of glucose into blood
glycogenesis
Formation of glycogen from other carbs, especially glucose
glycogenolysis
Breakdown of glycogen to glucose
gluconeogenesis
Conversion of fats or proteins into glucose
regulation of gas concentrations
− Oxygen for respiration, CO2 waste product
− Lungs exchange gases
control of breathing
− Intercostal muscle and diaphragm: skeletal muscle these require nerve impulses to create contraction.
− Diaphragm stimulated by the phrenic nerve and intercostal muscle stimulated by intercostal nerve
− Origin of nerve in spinal cord (nerve)
− If injury results in paralysis of muscle, this results in death
− Control by respiratory center muscles in medulla oblongata
− There are 2 regions; one that controls the expiration and one that controls the inspiration
− To coordinate breathing, messages need to pass back and forth between the neurons of these 2 regions
− Oxygen and carbon dioxide are carried in blood and concentrations affect breathing rate
oxygen concentration
− If concentration of oxygen falls below normal and other factors remain then the breathing rate increases
− Concentration has to fall to very low levels before it has a major effect
− Chemoreceptors that are very sensitive to changes in the oxygen concentration in the blood plasma are known as aortic and carotid bodies
− A large decrease in oxygen concentration stimulates the chemoreceptor’s and nerve impulses are transmitted, so breathing rate increases
carbon dioxide concentration
− Major factor in regulation of breathing rate
− Any small increase in the concentration of carbon dioxide is enough to cause an increase in rate of breathing
hydrogen ion concentration
− As the hydrogen ion concentration of the blood increase, pH decrease, causing an increase in the breathing rate
− Decrease in pH stimulates chemorecpetors in the aortic and carotid bodies, which then transmit impulses to the respiratory centre, resulting in an increase in the breathing rate
voluntary control of breathing
− Humans are able to voluntary control their rate and depth of breathing , factors very important in speech
− We can stop breathing for a limited time
− Rapid , deep breathing can provide more oxygen than required and remove more carbon dioxide than necessary, this is called hyperventilation
exercise and breathing
− During exercise the contracting muscle cells require large amounts of oxygen and produce large amounts of carbon dioxide
− In responding to this increased demand for gas exchange, the respiratory system increases both the rate of breathing and the depth of breathing
heart rate and blood pressure
− Output of blood from the heart is therefore crucial to maintaining homeostasis of gases and body fluids
− The heart rate is the number of times the heart beats per minutes, while the stroke volume is the volume of blood from the heart with each contraction
− Cardiac output is a combination of the 2 and is the amount of blood leaving the heart every minute
Cardiac output (mL/min) = heart rate (beats/min) X stroke volume (mL)
− Blood pressure is the force with which the blood presses on the walls of the blood vessels
the blood pressure at a particular time depends on
− The cardiac output - as cardiac output increases so does blood pressure
− The diameter of blood vessels - constriction of blood vessels increase pressure and dilation decreases blood pressure
regulation of heart rate
− The bundles of specialised cells controlling the hearts activity are called the sinoatrial node (SA node) and the atriocentricular node (AV node)
− SA node is responsible for the rhythmical contractions
heart beat - sequence of events
- The SA node sends out nerve impulses that spread through the atria
- The stimulus reaches the AV node. At about this time, contraction of the muscle of the atrium begins
- Stimulation of the Av node causes it to send out its own impulses. These travel down the fibres in the septum between the ventricles
- The impulses then spread through the muscles of the ventricles. Atrial contraction is now complete and ventricular contraction begins
