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Lipid-soluble Hormone Action
1. the hormone diffuses into the cell.
2. If the cell is a target cell for that hormone, the hormone can bind to a receptor and create a receptor-hormone complex within the cytosol of the nucleus.
3. This complex can alter the gene expression of the cell by turning to genes encoded by the cell's DNA on or off. Depending on the type of receptor the hormone binds to, it can be excitatory or inhibitory in that cell. The end result is the alteration of the cells activity.
Water-soluble Hormone Action
- The hormone (1st messenger)attaches to receptors on the plasma membrane of the target cell.
- Receptor-hormones complex activates a G protein
- G protein activates adenylate cyclase
- Adenylate cyclase converts ATP to cyclic AMP (cAMP) (2nd messenger) in the cytoplasm
- cAMP activates enzymes (protein kinases) which bring about the desired effect within the cell. Remember, kinases phosphorylate(add a phosphate to) other molecules
- -2nd messengers can act as activators, inhibits, or cofactors
- Ca++ is also a common 2nd messenger.
- to limit the duration of the response, unless new hormone binds to the receptors, an enxyme called pohosphodiesterase inactivates cAMP.
Hormone secretion is signaled and regulated by a number of different mechanisms:
- Signals from the nervous system
- chemical fluctuations in the blood
- and the secretion of other hormones (from another organ)
True or False
Most hormone systems work via negative feedback
few work by positive feedback
The hormone output reverses a particular stimulus
The hormone output encourages and reinforces the stimulus.
For most hormone systems to function correctly it is necessary to have:
- -Receptors for stimulus
- -Interpretation(control) center
- -and an initiated response
- -For example receptors in the pancreas detect changes in the blood glucose level
- -If it is high the the pancreas secretes insulin.
- -The increased level of insulin results in the increased production of glucose transporters, thereby facilitated the uptake of glucose into the cells.
- -This decreases the blood glucose level.
Target Cell responsiveness depends on:
- The hormone concentration
- The abundance of the target-cell receptors
- The Influence of other hormones
- -Permissive effect
- -Synergistic effect
- -Antagonistic effect
A ______ _____ can react more energetically if there is a high level of hormone or the cell has ___-______
Target cell, up-regulated
The action of one hormone requires the presence of another hormone
the effect of two hormones acting together is greater than on acting alone
One hormone opposes the action of another hormone.
The Pituitary and the Hypothalamus
- the hypothalamus is the major link between the nervous and endocrine systems.
- -it receives input from several regions in the brain: limbic, RAS, thalamus, etc.
- The hypothalamus controls the pituitary gland (hypophysis).
- The pituitary gland hangs down from the hypothalamus on a stalk called the infundibulum.
What are the two lobes of the pituitary gland?
- The anterior lobe is called adenophypophysis (about 75%of the total pituitary weight)-functionally connected to the hypothalamus by blood vessels
- The posterior lobe of the pituitary, also called the neurohypophysis
see objective 9 p. 654-655
Posterior pituitary or neurohypophysis
- consists of special axons and axon terminals from neurosecretory neurons.
- does not synthesize any hormones
- the hormones from the posterior pituitary are produced by neurosecretory cells within the nuclei of the hypothalamus and secreted down the axons with vesicles to be stored and later released from the posterior pituitary.
- hormones from the hypothalamus that stimulate the "release" of hormones form the anterior lobe of the pituitary (adenohypophysis)
- If "releasing" is in the name of the hormone, it comes from the hypothalamus
Hormones form the hypothalamus that inhibit the release of hormones from the adenohypophysis (anterior lobe of the pituitary)
- hormones from the adenohypyphysis
- it is released from one endocrine gland and targets another
- the term tropic may also be used in the name of the specific cells that secrete it: thyrotrophs, corticotrophs, gonadotrophs, are all cells of the pituitary that secrete a particular hormone that targets another gland.
Anterior pituitary hormones
see objective. 11 p. 657
Most hormone disorders involve having insufficient release (_________) or excessive secretion (________) of hormone.
- Too little hormone production
- Decreased hormone receptors
- second-messenger system defects
- Lack of hormone precursors
- Degraded hormones
- Poor blood flow (ischemia)
- Excessive hormone production
- Tumors of endocrine origin- causing excess hormone release. Benign or malignant
- Absence of normal feedback mechanisms
- caused by insufficient hGH release during childhood (hyposecretion)
- Without hGH, the epiphyseal plates will close before the child achieves a normal adult height
- The deficient growth of tissue will affect all of the body systems
- however the child will have normal body proportions.
- caused by hypersecretion of hGH during childhood
- overall body proportions will remain consistent but the person will be very tall
- The main cause is is a tumor of the anterior pituitary. detection and treatment techniques have made giantism fairly rare.
- a disorder caused by excessive hGH secretion in adulthood after a person is done growing.
- -Enlargement of and elongation of he bones of the face, jaw, cheek, and hands
- -The long bones of the extremities are unaffected because the growth plates are already closed
- -commonly caused arthritis and carpal tunnel syndrome due to excess tissue growth.
- Diabetes means to overflow or siphon; it relates to the development of polyuria (too much urine production)
- Insipidus means tasteless
- so putting these two terms together means "the production f too much tasteless urine"
- There are two types
- -Neurogenic- insufficient production or secretion of ADH
- -Nephrogenic- Diminished renal response to the ADH that is produced
- With limited amounts of ADH, the patient will not reabsorb water, therefore they will secrete large volumes of very dilute urine.
The thyroid gland
- Located just inferior to the larynx, specifically the thyroid cartilage (Adam's apple)
- It is butterfly shaped and consists of two lobes, the left and right
- The tissue connection between the two lobes is called the isthmus
- Microscopically the thyroid is made up of small spherical sacs called thyroid follicles
- These make up the largest portion of the glands mass.