Lecture Objectives - Weebly



Lecture Objectives

Endocrine System

Discuss the differences between neural and endocrine mechanisms of control of body functioning.

• Both systems work together & both respond to a stressor

• Nervous system

o Rapid response, but lasts for a short period of time

o Electrical impulse

o Regulates excitable tissues like skeletal, muscle, cardiac, and glands

• Endocrine system

o Slow response, but lasts for a longer time

o Chemical impulse

o Chemicals distributed in bloodstream (hormones) that affect metabolic activity of target cells

Differentiate exocrine and endocrine glands.

• Exocrine glands

o Ducts

o Not hormonal

o Involved with digestive processes

o Ex: sweat, oil, and salivary glands

• Endocrine glands

o Ductless

o Secrete hormones

o Highly vascularized glands

o Travel in bloodstream

Identify the neuroendocrine link, and discuss its functioning.

• 2 components

o “neuro” component = hypothalamus

o “endocrine” component = pituitary gland

▪ referred to as the master gland (especially the anterior region)

o the posterior pituitary extends off of the infundibulum connected to the hypothalamus

List and differentiate the types of chemical messengers.

• Hormones

o Long distance chemical messengers

o Produced in one part of the body, but exert effect in another part of the body

• Autocrines

o Very localized signaling molecule

o Chemicals produced by cell that change activity of that cell

• Paracrines

o Localized

o Chemical signals secreted by cells that affect neighboring cells

• Pheromones

o Chemical secretion produced by one individual that affects another individual

o Produced in sweat

o Used for mating/sexual attraction

Identify the cells at which hormones exert their effects, and discuss the generalized effects hormones can produce.

• Target cells

o Receptor cells that alter the activity of the cell

• Generalized effects hormones can produce:

o Changes in permeability (open and close ion channels)

o Production of new proteins aka protein synthesis

o Activate or deactivate preexisting enzymes in the cell to change activity

o Promote secretion

▪ Activation of the cell causes it to secrete some sort of product

o Stimulate mitosis

Describe the chemical classifications of hormones.

• Amino acid based (non-steroid)

o Water soluble

o Use G proteins and secondary messengers

o Very common

o Derived from amino acids

o Receptor is outside of cell

• Steroid

o Fat soluble

o Direct activation

o Less common

o Derived from cholesterol

o Receptor outside cell

o Produced in cortex of adrenal gland or gonads

• Eicosanoid

o Biologically active lipid released by a cell to produce a localized effect

o More of a molecule than a hormone

o Important to remember that these are not technically hormones

Describe the two major mechanisms by which these two classes of hormones bring about their effects.

• Steroid action (produce new proteins)

1. Hormone diffuses through plasma membrane

2. Bind to intracellular receptor inside the cell

3. Activated complex binds to receptor protein on DNA

4. Promotes transcription

5. mRNA gets translated

6. Produces proteins

• Non-steroid action (amino acid based)

o Nothing new is being produced but the activity is changes

o 2 different mechanisms (cyclic AMP mechanism & PIP-calcium mechanism)

Discuss the two models of amino acid-based action. (MEMORIZE)

• Cyclic AMP mechanism

1. Hormone binds to membrane receptor

2. Modified receptor binds to G protein

3. G-protein gets activated

4. It activates adenylate cyclase

5. Adenylate cyclase generates cAMP

6. Protein kinase reactions

7. Phosphorylation of proteins which causes the activation or deactivation of proteins

8. Degrading of cAMP by phosphodiesterase

• PIP-calcium mechanism

1. Hormone binds to membrane receptor

2. Modified receptor binds with G protein

3. G protein gets activated

4. Activated G-protein activates phospholipase

5. Phospholipase splits PIP2 into DAG and IP3

6. DAG activates protein kinases

7. IP3 triggers release of calcium from ER

8. Calcium acts as additional second messenger

Identify the factors that control hormone action.

• Hormone level in bloodstream

• Number of receptors in/on target cells

• Receptor affinity

List three kinds of interaction that different hormones acting on the same target cell can have.

• Permissiveness

o Presence of a second hormone causes the first one to do more or exert its full effect

• Synergism

o More than one hormone produces same effect so combined effect if both are present is greater

o Ex: glucagon and epinephrine both regulate blood sugar levels in the same way, so if both are present there is a greater increase in blood sugar levels

• Antagonism

o Work in opposition to one another

o Ex: glucagon & insulin

Explain how hormone release is regulated.

• Hormone release is modified by the nervous system

• Most endocrine gland stimulation is inhibited by negative feedback loops

• 3 modes of stimulation/regulation

o humoral: change in concentration of something in the blood

o neural: stimulated by the nervous system to start producing

o hormonal: some are target tissues for the production of other hormones

List the major endocrine organs, and describe their body locations.

[pic]

Discuss the structure of the neurohypophysis, and describe the effects of its two hormones.

• Posterior pituitary

• Neural tissue

• Antidiuretic hormone (ADH)

o Regulates water balance

o Causes kidney tubules to reabsorb water to modulate how much is lost in urine

o Prevents urine formation

o Ex: instead of water leaking out of our bodies as urine, we reabsorb into bloodstream

• Oxytocin (OT)

o Stimulates smooth muscle contractions (childbirth & milk ejection)

o Promotes affectionate behavior

o Nicknamed the “cuddle hormone”

List and describe the adenohypophyseal hormones and their effects.

• Anterior pituitary

• Glandular/neural tissue

• Secretory

• Growth hormone (GH)

o Stimulates cell growth and division, protein synthesis, fat metabolism, and promotes glucose conservation

▪ Increase in GH in children = gigantism

▪ Decrease of GH in children = pituitary dwarfism

▪ Increase of GH in adults = acromegaly

▪ Decrease of GH in adults = AGHD

o GH cascade

1. Hypothalamus secretes GHRH

2. Activates the somatotropic cells of anterior pituitary and begins making GH

3. GH has both direct and indirect effects on tissues

4. Circulating GH triggers production of GHIH that stops GH secretion

5. Production of GH stops

o Direct actions of GH

▪ Increases blood levels of fatty acids

• Fats stored in the boy are released from fat storage & the lipids are put into circulation

▪ Decreases rate of glucose uptake and metabolism

▪ Stimulates the production of glycogen in the liver

▪ Encourages the breakdown & release of glucose and glycogen in the liver

• Called the diabetagenic effect

o Indirect actions of GH

▪ Operate through IGFs (insulin-like growth factor)

• Stimulate the uptake of amino acids from the blood to enter cells and be converted into cellular proteins

• Stimulate uptake of sulfur and deposit into matrix or cartilage

• TSH

o Activates the thyroid gland

o Target cells are the thyroid gland

o Thyrotropin hormone

o TSH cascade

1. Hypothalamus sends TRH to anterior pituitary

2. TRH causes the thyrotrope cells to produce TSH

3. Increased levels of TSH inhibit both the pituitary and hypothalamus from secreting TRH

• Also stimulate GHIH

• ACTH

o Stimulates the adrenal cortex to release corticosteroid hormones

▪ Especially the glucocorticoids-related to blood glucose levels

o Target cells of ACTH are the adrenal cortex

o This is a tropic hormone

o Main function of adrenal gland is to reduce stress

o Pituitary hormone

o ACTH cascade

1. Hypothalamus secretes CRH (corticotrope releasing hormone)

• Fever, hypoglycemia, and stressors promote CRH release

2. CRH stimulates corticotrope cells within the anterior pituitary to release ACTH

3. Increased levels of glucocorticoids stop secretion of CRH

4. Therefore, ACTH secretion stops

o CRH release is prompted by cold, pregnancy, or stress

• Gonadotropins

o Produced by the anterior pituitary gland

o Regulate the function of gonads

o Includes FSH and LH hormones

▪ FSH (follicle stimulating hormone): stimulates gamete production

• Sperm and egg

▪ LH (lutenizing hormone): promotes production of gonadal hormones

• Testosterone and estrogen/progesterone

▪ Both genders produce both hormones

o Male

▪ FSH stimulates sperm production

▪ LH stimulates interstitial cells of testes to produce testosterone

o Female

▪ FSH stimulates egg production

▪ FSH & LH regulate follicle maturation

▪ LH triggers ovulation and stimulates synthesis of the ovarian hormones: estrogen and progesterone

o Gonadotropin cascade

1. At puberty, the hypothalamus begins to secrete GnRH

2. GnRH stimulates the gonadotrope cells of the pituitary to secrete gonadotropins

3. The released gonadotropins cause the gonads to mature and begin producing hormones

4. Increased levels of gonad hormones suppress the secretion of FSH and LH

• Prolactin (PRL)

o Main role: stimulate milk production by the breasts

o Enhance testosterone production in males (level of prolactin in males is low)

o Prolactin cascade (cycling/not pregnant)

1. High estrogen levels stimulate lactotrope cells to release prolactin by suppressing the production of PIH

2. The prolactin production is brief due to ovarian hormone cycling

3. Low estrogen levels cause hypothalamus to produce PIH

• Lactation does not occur because low estrogen levels inhibit prolactin production and high estrogen levels did not last long enough for lactation to occur

4. This causes prolactin production to stop production

o Prolactin cascade (pregnant)

1. High estrogen levels stimulate the release of PRL

• Estrogen levels are high during pregnancy (unlike during cycle)

• PRL is triggered near end of pregnancy

• Suckling maintains prolactin production

• Lack of suckling results in the return of the normal hormonal cycle, causing PIH production

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