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IB Biology: Endocrine System
Transcript of IB Biology: Endocrine System
It produces the hormone melatonin, a naturally-occurring antioxidant that helps regulate the body’s circadian rhythm. What are hormones? Hormones are chemicals that produced by endocrine glands and travel via blood to the tissues of the body. Assessment Statements 6.7 State that the endocrine system consists of glands that release hormones that are transported in the blood.
6.8 State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.
6.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback
6.10 Explain the control of body temperature, including the transfer of heart in blood, and the roles of the hypothalamus, sweat glands, a skin arterioles and shivering.
6.11 Explain the control of blood glucose concentration, including the roles of glucagon, insulin and alpha and beta cells in the pancreatic islets.
6.12 Distinguish between type I and type II diabetes. Peptide Hormones Homeostasis Hypothalamus and Pituitary Hormonal Control Endocrine System State that hormones are chemical
messengers secreted by endocrine
glands into the blood and transported
to specific target cells. H1.1 State that hormones can be steroids,
proteins and tyrosine derivatives, with
one example of each. H1.2 Distinguish between the mode
of action of steroid hormones and
protein hormones. H1.3 Outline the relationship between
the hypothalamus and the pituitary
gland. H1.4 Explain the control of ADH
(vasopressin) secretion by negative
feedback. H1.5 Endocrine system: series of glands that produce and secrete hormones thalamus
testis Slower and longer acting than Nervous system
Secretes into bloodstream: no ducts like exocrine glands, more vascularized tissue Hypothalamus - The hypothalamus is a part of the brain near the optic chiasm.
suppresses the release of hormones in the pituitary gland
Controls water balance, sleep, temperature, appetite and blood pressure. Pituitary - The pituitary gland is located at the base of the brain. No larger than a pea, it gland controls many functions of the other endocrine glands Thyroid and parathyroid glands - The thyroid and parathyroid glands are located in front of the neck, below the larynx (voice box).
The thyroid plays an important role in the body's metabolism.
Both the thyroid and parathyroid glands also play a role in the regulation of the body's calcium balance Thymus - The thymus is located in the upper part of the chest and produces T-lymphocytes (white blood cells that fight infections and destroy abnormal cells). Adrenal glands - The two adrenal glands are located on top of both kidneys. They work hand-in-hand with the hypothalamus and pituitary gland Kidney - The two kidneys are located near the middle of the back, just below the rib cage.
They process the blood to sift out waste products and extra water. This waste and extra water becomes urine, which is stored in the bladder. Pancreas - The pancreas is located across the back of the abdomen, behind the stomach.
The pancreas plays a role in digestion, as well as in hormone production Ovary - A female's ovaries are located on both sides of the uterus, below the opening of the fallopian tubes (tubes that extend from the uterus to the ovaries).
In addition to containing the egg cells necessary for reproduction, the ovaries also produce estrogen and progesterone. Testis - A male's testes are located in a pouch that hangs suspended outside his body. The testes produce testosterone and sperm. Proteins with hormone function synthesized from Amino acids from DNA template inside the cell nucleus prolactin, ACTH, growth hormone, antidiuretic Hormone (ADH), oxytocic, cholesystokinen, gastrin, insulin ADH, ACTH, Growth Hormone, Leutenizing hormone, FSH, oxytocin, prolactin, Thyroid stimulating hormone (TSH) Parathyroid hormone....Thyroid hormone and calcitonin aldosterone, cortisol, epinephrine glucagon and insulin Renin, erythropoietin estrogen, progesterone testosterone water soluble BUT cannot pass thru plasma membrane
bind to surface receptor
secondary messenger released intot the cell (cAMP)
secondary messenger activates or inhibits enzymes Steroid Hormones lipid soluble, CAN pass thru plasma membrane
bind to receptor inside cell to form hormone-receptor complex
regulates gene transcription contain cholesterol androgens, estrogens, progestins, corticoids Tyrosine derived Hormones there are two classes of hormones that are derived from the amino acid tyrosine thyroid hormones
catecholemines fast acting, small amts required slow acting, larger amts required http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP13704 thyroxine, epinepherine, norepinepherine, melatoinin (epi, norepi) water soluble BUT can pass thru cell membrane lipophillic water soluble Blood and tissue fluid (derived from blood) make up the internal environment.
This internal environment varies very little compared to the external environment which varies greatly.
Negative feed back is used to keep the internal environment between limits. Homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance. It uses the nervous and endocrine system to do so. It has a stabilising effect as any change from a set point level will result in an opposite change. The levels of production of for example blood glucose, feed back to affect the rate of production. If blood glucose levels rise above the set point, this will feed back to decrease production and reduce the level back around the set point. A decrease in blood glucose levels below the set point will result in an increase in production so that the levels increase back to the set point. Small fluctuations around the set point will not cause any response. Negative feed back is only triggered when there are significant increases or decreases from the set point. NEGATIVE FEEDBACK LOOP receptor
effector Body Temp receptors in skin and hypothalamus (core temperature of blood) heat loss center of hypothalamus heat conservation center of hypothalamus blood vessels constrict
skeletal muscles activate
erector pili muscles contract
adrenaline and thyroxin released to increase metabolic activity in some tissues blood vessels dialate
sweat glands activated
erector pili muscles relax effectors control center in the brain Blood Glucose Regulation Glucose is the transport carbohydrate in animals, and its concentration in the blood affects every cell in the body.
Its concentration is therefore strictly controlled within the range 0.8 – 1g per dm3 of blood,
very low levels (hypoglycemia) or very high levels (hyperglycemia) are both serious and can lead to death. Blood glucose concentration is controlled by the pancreas.
The pancreas has glucose receptor cells which monitor the concentration of glucose in the blood
It also has endocrine cells (called the Islets of Langerhans), which secrete hormones.
The α-cells secrete the hormone glucagon
The β-cells secrete the hormone insulin.
These two hormones are antagonistic, and have opposite effects on blood glucose effectors insulin stimulates the uptake of glucose by cells for respiration, and in the liver it stimulates the conversion of glucose to glycogen (glycogenesis).
It therefore decreases blood glucose glucagon stimulates the breakdown of glycogen to glucose in the liver (glycogenolysis), and in extreme cases it can also stimulate the synthesis of glucose from pyruvate.
It therefore increases blood glucose anaerobic respiration blood glucose pancreas islet beta cells release insulin liver cells convert blood glucose to glycogen other body cells uptake glucose
adipose cells take in glucose = fat blood glucose pancreas islet alpha cells release glucogon liver cells break down stored glycogen to glucose, amino acids to glucose blood glucose falls blood glucose rises negative feedback negative feedback core body temp typically around 37 celcius blood carries HEAT! conserve heat by keeping blood near the core, get rid of heat by running blood in the extremities close the surface **evaporation is cooling via convection Diabetes Mellitis Type I diabetes (early or juvenile onset):
■Auto-immune disease in which the beta-cells pancreatic are destroyed.
■Unable to produce insulin.
■Responds well to regular injection of insulin probably manufactured as the genetically engineered humulin. Type II diabetes (Adult onset):
■Reduced sensitivity of the liver cells to insulin.
■Reduced number of receptors on the liver cell membrane In both types of diabetes there is:
■a build of glucose in the blood stream and it will then subsequently appear in urine.
■High concentrations of blood glucose (hyperglycaemia) results in the movement of water from cells by osmosis.
■This extra fluid in the blood results in larger quantities of urine production.
■A lack of glucose in cells means that fats then proteins have to be metabolized in respiration.
■Particularly the breakdown of protein for energy creates organ damage The hypothalamus has many receptors for changes of internal conditions and serves as a link between the nervous system and the endocrine system (pituitary). Below the hypothalamus is a double lobed structure called the pituitary that produces the endocrine secretions when stimulated by the hypothalamus. The hypothalamus controls each lobe of the pituitary slightly differently. Control of Anterior Lobe
■Hormones are sent from the hypothalamus to the anterior pituitary via a blood vessel called the portal vein.
■The hypothalamus acts as the endocrine gland (a)
■Hormone travel in blood through the blood vessel (portal vein)(b).
■The target tissue is the anterior lobe of the pituitary(c). e.g. LH, TSH and FSH Control of Posterior Lobe of the pituitary
(d) Neuro-hormones are synthesised in the hypothalamus neuron. They are transported and stored in vesicles in the axon ending located in the posterior pituitary.
(e) Nerve impulses travel down the axon into the posterior pituitary. This causes the release of the vesicles of hormones into the blood stream at the posterior pituitary. e.g. Oxytocin, ADH TRH: thyrotropin releasing hormone
stimulates release of thyoid stimulating hormone and prolactin from the ant pituitary
■The homeostatic regulation of water (osmoregulation) is brought about by the action of the hormone Anti-diuretic hormone.
The hypothalamus is sensitive to changes in plasma concentrations.
■Neurosecretory cells in the hypothalamus synthesis ADH and transport this along the axon of their nerves for storage in their synaptic knob endings in the posterior lobe of the hypothalamus.
When plasma osmolarity is below a certain threshold, the osmoreceptors are not activated and secretio of antidiuretic hormone is suppressed. When osmolarity increases above the threshold, the ever-alert osmoreceptors recognize this as their cue to stimulate the neurons that secrete antidiuretic hormone
■Osmoregulatory sensitive cells in the hypothalamus which are sensitive to plasma concentrations stimulate the neurosecretory cells to transmit impulses to their storage regions in the posterior lobe of the hypothalamus.
■ADH is secreted and has its target tissue of the Distal Convoluted and Collecting tubules of the kidney.
■The ADH causes the opening of the Aquaporin (pores) which increases water reabsorption from kidney filtrate. This is an example of the how the hypothalamus and the posterior pituitary integrate to control the release of another hormone Neurohormones: hormones released by neurons
• Thyrotropin-releasing hormone (TRH)
• Gonadotropin-releasing hormone (GnRH)
• Adrenocorticotropin-releasing hormone
• Antidiuretic hormone (ADH) TRH: Thyrotropin Releasing Hormone released by neurons of Hypothalamus
travel to Ant. Pituitary via portal vessel
stimulate release of TSH and prolactin by Ant. Pituitary cells
TSH: effect on Thyroid, metabolism somatostatin: inhibits formation of TSH
Dopamine: inhibits prolactin Gonadotropin Releasing Hormone Released by neurons in the hypothalamus
travels to Ant. Pituitary via portal vessel
stimulates release of LH (leutenizing Hormone) and FSH (follicle stimulating Hormone) from the ANT Pit. hi frequency pulses: LH
Low frequency pulses: FSH
Constant in males, fluctuates with cycle in females
Responsible for follicular development, ovulation and spermatogenesis Corticotropin Releasing Hormone released by neurons of the hypothalamus
travels to Ant pit via protal vessels
stimulates release of ACTH (adrenocorticotropic hormone)
stimulates adrenal glands to release a multitude of hormones cortisol (main glucocorticoid), mineralcorticoids fight or flight •heart rate and blood pressure increase
•pupils dilate to take in as much light as possible
•veins in skin constrict to send more blood to major muscle groups (responsible for the "chill" sometimes associated with fear -- less blood in the skin to keep it warm)
•blood-glucose level increases
•muscles tense up, energized by adrenaline and glucose (responsible for goose bumps -- when tiny muscles attached to each hair on surface of skin tense up, the hairs are forced upright, pulling skin with them)
•smooth muscle relaxes in order to allow more oxygen into the lungs
•nonessential systems (like digestion and immune system) shut down to allow more energy for emergency functions
•trouble focusing on small tasks (brain is directed to focus only on big picture in order to determine where threat is coming from) such as aldosterone: controls mineral uptake esp in kidneys glucose metabolism and reduce inflammation adrenal gland also releases: androgens and catecholamines such as epinepherine Nervous system ■A neuron has a cell body with extensions leading off it. ■Numerous dendrons and dendrites provide a large surface area for connecting with other neurons, and carry nerve impulses towards the cell body.
■A single long axon carries the nerve impulse away from the cell body.
■The axon is only 10µm in diameter but can be up to 4m in length in a large animal (a piece of spaghetti the same shape would be 400m long)!
■Most neurons have many companion cells called Schwann cells, which wrap their cell membrane around the axon many times in a spiral to form a thick insulating lipid layer called the myelin sheath.
■Nerve impulse can be passed from the axon of one neuron to the dendron of another at a synapse. A nerve is a discrete bundle of several thousand neuron axons. Humans have three types of neuron:
■Sensory neurons have long axons and transmit nerve impulses from sensory receptors all over the body to the central nervous system.
■Motor neurons also have long axons and transmit nerve impulses from the central nervous system to effectors (muscles and glands) all over the body.
■Interneurones (also called connector neurons or relay neurons) are usually much smaller cells, with many interconnections. ■There are various receptor around the body such as skin and the eye.
■Stimuli (think of them as energy forms) are detected by the receptors and turned into an nerve impulse (chemical energy).
■Nerve impulses from sensory nerves are conducted to the central nervous system along sensory neurons.
■The impulse is sent to the relay neurons that move it around inside the central nervous system (brain and spine). •Motor neurons take the relayed nerve impulse to the effectors (often muscles) which then produce the response. ■This is a cross section through the vertebrate spinal column.
■The receptor is deep in the biceps muscle.
■Sensory neuron conducts nerve impulses from the receptor to the central nervous system.
■The relay nerve conduct the impulse through the spinal cord and in a reflex back to the motor neuron.
■The motor neuron connects to the effector which in this case is the biceps muscle Define resting potential and action potential (depolarization and repolarization).( ■
To record the electrical activity of a nerve it is placed in an isotonic fluid bath.
A reference electrode is placed in the surrounding fluid.
A recording electrode is inserted into the cytoplasm of the axon.
The electrical disturbances are measured and displayed on the oscilloscope ■
Resting potential is the negative charge registered when the nerve is at rest and not conducting a nerve impulse.
Action potential is the positive electrochemical charge generated at the nerve impulse. Normally this is seen as the 'marker' of the nerve impulse position.
Depolarisation is a change from the negative resting potential to the positive action potential.
Re-polarisation is the change in the electrical potential from the positive action potential back to the negative resting potential. membrane potentials To understand the Resting Potential and Action Potential first consider an ion pump found in the plasma membrane Sodium-Potassium ATPase
This uses the energy from ATP splitting to simultaneously pump 3 sodium ions out of the cell and 2 potassium ions in.
If this was to continue unchecked there would be no sodium or potassium ions left to pump, but there are also sodium and potassium ion channels in the membrane.
These channels are normally closed, but even when closed, they “leak”, allowing sodium ions to leak in and potassium ions to leak out, down their respective concentration gradients.
The combination of the Na +K +ATPase pump and the leak channels cause a stable imbalance of Na + and K + ions across the membrane.
This imbalance causes a potential difference across all animal cell membranes, called the membrane potential.
The membrane potential is always negative inside the cell, and varies in size from –20 to –200 mV in different cells and species.
The Na +K+ ATPase is thought to have evolved as an osmoregulator to keep the internal water potential high and so stop water entering animal cells and bursting them. Plant cells don’t need this as they have strong cells walls to prevent bursting. Resting Potential & Action Potential
In nerve and muscle cells the membranes are electrically excitable, which means that they can change their membrane potential, and this is the basis of the nerve impulse.
The sodium and potassium channels in these cells are voltage-gated, which means that they can open and close depending on the voltage across the membrane.
Early experiments on nerves focused on the non-myelinated Squid Giant Axon .
An electrodes is placed inside the cell and one outside the cell (reference).
The electrodes are attached to an oscilloscope
The nerve cell is stimulated to generate a nerve impulse and the voltage change recorded on the oscilloscope ■
The normal membrane potential of these nerve cells is –70mV (inside the axon), and since this potential can change in nerve cells it is called the resting potential.
When a stimulating pulse was applied a brief reversal of the membrane potential, lasting about a millisecond, was recorded. This brief reversal is called the action potential:
RP: Resting Potential
AP: Action Potential
RFP: Refractory Period
TH: Threshold The Action Potential has two stages depolarisation (DP) and Re-polarisation(ReP) Depolarisation .(DP)
The stimulating electrodes cause the membrane potential to change a little.
The voltage-gated ion channels can detect this change, and when the potential reaches –30mV(TH) the sodium channels open for 0.5ms
The causes sodium ions to rush in, making the inside of the cell more positive.
This phase is referred to as a depolarisation since the normal voltage polarity (negative inside) is reversed (becomes positive inside). Re-polarisation (ReP).
The membrane potential reaches 0V.
The potassium channels open for 0.5ms, causing potassium ions to rush out.
This makes the inside more negative again.
Since this restores the original polarity, it is called re-polarisation
How the nerve impulse travels along the axon:
Once an action potential has started it is moved (propagated) along an axon automatically. Section a) Refractory potential:
The axon is in a refractory (ReP)period which means that diffusion backwards of Na+ from the action potential is not able to depolarise the membrane channels. This means the impulse travels in one direction Section b) Action Potential:
The voltage gates have been opened and there is a high concentration of Na+ in the axon. This diffuses to the next set of voltage gates depolarising from resting potential Threshold (TH):
The ion channels are either open or closed; there is no half-way position. This means that the action potential always reaches +40mV as it moves along an axon, and it is never attenuated (reduced) by long axons. In other word the action potential is all-or-nothing. Re factory Period (ReP):
After an ion channel has opened, it needs a “rest period” before it can open again.
This is called the refractory period, and lasts about 2 ms.
This means that, although the action potential affects all other ion channels nearby, the upstream ion channels cannot open again since they are in their refractory period, so only the downstream channels open, causing the action potential to move one-way along the axon.
The delay caused by refractory period also prevents the summation of Action potentials (one impulse cannot catch up another impulse) Human Nerve propagation:
It should be noted that the description given above of nerve conduction is for a squid giant axon. This is a typical arrangement in the invertebrates. To increase the rate of nerve conduction the axon diameter is increased. However, vertebrates have a different method of accelerating their nerve conduction but this is not part of the IB syllabus for this particular unit. You can however read about this method of nerve conduction called saltatory conduction Section c: Resting potential:
The Na+will diffuse to this position. If the voltage reaches threshold (TH) then the channel will open Na+will flood in and a new action potential site will be established. Section c: Resting potential:
The Na+will diffuse to this position. If the voltage reaches threshold (TH) then the channel will open Na+will flood in and a new action potential site will be established.