The Endocrine System Flashcards
Definition of a Hormone
chemical that transfers information and instructions between cells in animals
What do hormones regulate?
- Growth and development
- Control the function of various tissues
- Support reproductive function
- Regulate metabolism (break down food to create energy)
Four types of hormone delivery
AUTOCRINE
- Feeds-back on the same cell
- Without entering blood circulation
PARACRINE
- Diffuses to its adjacent target cells
- Via immediate extracellular space
- Blood not directly involved
ENDOCRINE
- Delivered to target cells by blood circulation
NEUROENDOCRINE:
- Produced and released by a neuron
- Delivered to target cells by bloodstream
Four mechanisms of intercellular communication
DIRECT COMM
- Via gap junctions
- Involves ions, solutes, lipid-soluble materials
- Limited to adjacent cells of the same type
PARACRINE COMM
- Via extracellular fluid
- Involves paracrine factors
- Limited to a local area
ENDOCRINE COMM
- Via bloodstream
- Involves hormones
- Limited to tissues and organs with appropriate receptors
SYNAPTIC COMM
- Across synapses
- Involves neurotransmitter
Hypothalamus
- Produces regulatory hormones (pituitary gland)
- Produces ADH, OXT
Thyroid
- Location: Below the larynx
- Produces triiodothyronine (T3) and thyroxine (T4)
- Sets the basal metabolism rate
- Regulates body temperature
- Growth and development
-
Calcitonin (CT)
- Decreases calcium levels (store in bones)
Adrenal Glands
- Medulla
- Epinepherine
- Norepinephrine
- Cortex
- Cortisol
- Corticosterone
- Aldosterone
- Androgens
Pancreatic Islets
Alpha cells
- Secrete glucagon
- In response to low blood glucose
- Stimulates glycogenolysis and lipolysis
Beta cells
- Secrete insulin
- In response to high blood glucose
- Promotes entry of glucose into cells
- Promotes conversion of glucose into glycogen and fat
Pineal gland
- Location: Basal forebrain near thalamus
- Secretes melatonin
- In response to suprachiasmatic nucleus (SCN) of hypothalamus
- Regulates circadian rhythms
- Secreted at night and inhibited by light
Parathyroid gland
- 4 glands embedded in lateral lobes of post. side of thyroid gland
- Secrete Parathyroid hormone (PTH)
- Stimulates osteoclasts (break down bone) and inhibits osteoblasts (form new bone)
- ↑ osteoclasts releases Ca2+ from bone
- ↓ osteoblasts reduces rate of Ca2+ deposition in bone
- Enhances reabsorption of Ca2+ at kidneys
- Stimulates formation and secretion of calcitriol by the kidneys
Six organs with secondary endocrine function
HEART
-
ANP and BNP
- Decrease cardiac output
- Lowers blood pressure
THYMUS
-
Thymosins (atrophy during adulthood)
- Promotes T cell maturation
ADIPOSE TISSUE
-
Leptin
- Prevent overeating
DIGESTIVE TRACT
-
Ghrelin by stomach
- Stimulates hunger
-
CCK by small intestine
- Stimulates bile release
KIDNEYS
-
Erythropoetin (EPO)
- Stimulates production of RBC
-
Calcitriol
- Increases calcium levels
GONADS
- Testes: testosterone, inhibin
- Ovaries: estrogen, progesterone, inhibin
Three chemical classifications of hormones
-
Amino acid tyrosine
- Secreted by thyroid (T3, T4, CT)
- Or adrenal medulla (Epinepherine, norepinepherin)
-
Proteins and Peptides
- Anterior and posterior pituitary glands
- Pancreas (insulin, glucagon)
- Parathyroid gland
-
Steroids
- Adrenal cortex (cortisol, aldosterone)
- Ovaries, testes, and placenta
Prohormones and prehormones
- Prohormones are precursors of hormones, e.g. proinsulin
- Prehormones are precursors of prohormones, e.g. preinsulin
Nervous system VS Endocrine system
NERVOUS SYSTEM
- “Wired” with structural arrangement
- Releases neurotransmitters into synaptic cleft
- Short distance
- Rapid response
- Brief duration of action (eg reflexes)
ENDOCRINE SYSTEM
- “Wireless” system
- Releases hormones into bloodstream
- Long distance
- Slow response
- Long duration of action
Two mechanisms of hormone action
HYDROPHOBIC (Steroid) hormones
- Receptors in target’s cytoplasm or nucleus
- Can diffuse thru plasma membrane
- Targets nucleus to affect transcription
- Genomic action
- Takes at least 30 mins
HYDROPHILIC (Peptide) hormones
- Receptors on surface of target cell
- Act through 2nd messengers
- Quick effects
Describe the bind to nuclear hormone receptors for hydrophobic hormone action
- Travel in blood attached to carrier proteins
- Dissociate from carriers to pass thru plasma membrane
- Bind to nuclear hormone receptors in the cell
- Serve as transcription factors to activate transcription
- Superfamily: Steroid family and thyroid hormone
Describe the adenylate cyclase-cAMP second messenger system in hydrophilic hormones
1) Hormone binds to receptor
2) Activates G-protein
3) Activates adenylate cyclase
4) Enzyme converts ATP into cAMP
4) cAMP activates protein kinase A
5) PKA phosphorylates enzymes that produce
hormone’s effects
6) cAMP inactivated by phosphodiesterase
Adrenaline binding to beta receptors
Describe the phospholipase-C-Ca2+ second messenger system in hydrophilic hormones
1) Hormone binds to receptor
2) Activates G-protein
3) Activates phospholipase C
4) Phospholipase C splits phospholipid into 2nd messengers IP3 and DAG
5) IP3 binds on endoplasmic reticulum receptors
6) Ca2+ channels open
7) Calcium released into the cytoplasm
8) Activates calmodulin
9) Activates protein kinase C
10) PKC adds phosphates to proteins altering enzyme activity
e.g. glycogen → glucose-1-phosphate → glucose 6 phosphate → glucose → blood
Adrenaline binding to alpha receptors
Describe the tyrosine kinase second messenger system in insulin
1) Insulin binds to receptor
2) Receptor = enzyme called tyrosine kinase
3) Alpha subunit of receptor sticks out on extracellular side, beta subunit embedded within plasma membrane
4) Insulin binds to alpha subunit of receptor
5) Two receptor units come together (dimerization)
6) Beta subunits phosphorylate eo
7) Activated tyrosine kinase phosphorylates other molecules
e.g. signals molecules to induce hormone/growth factor effects
The six hormones produced by the anterior pituitary gland
Produces own hormones controlled by the hypothalamus
- Growth hormone promotes growth, protein synthesis, and movement of amino acids into cells
- Thyroid stimulating hormone stimulates thyroid to produce and secrete T4 and T3
- Adrenocorticotropic hormone stimulates adrenal cortex to secrete cortisol
- Follicle stimulating hormone stimulates growth of ovarian follicles and sperm production
- Luteinizing hormone causes ovulation and secretion of testosterone in testes
- Prolactin stimulates milk production by mammary glands
Cortisol pathway
- Hypothalamus releases corticotrophin-releasing hormone (CRH)
- Stimulates anterior pituitary to produce adrenocorticotropic hormone (ACTH)
- Stimulates adrenal cortex to release cortisol
What is cortisol?
- Steroid hormone
- Regulates circadian rhythm
- 80% carried in blood by cortico-steroid binding globulin
- 15% bound to albumin
- 5% free in solution
- Main function
- Proteins broken down to amino acid
- Amino acid converted to glucose
- Nitrogen produced as by-product, excreted as urea
- Increases blood glucose
Describe the hypothalamic control of the posterior pituitary
- Hormones transported along hypothalamo-hypophyseal tract to posterior pituitary
- Release controlled in hypothalamus by neuroendocrine reflexes
ADH
- Supraoptic nuclei of hypothalamus produces ADH
- Promotes H2O conservation by kidneys
Oxytocin
- Paraventricular nuclei of hypothalamus produces oxytocin
- Stimulates contractions of uterus during parturition
- Stimulates contractions of mammary gland alveoli for milk-ejection reflex
The two classes of hypothalamic regulatory hormones in the anterior lobe
Releasing hormones (RH)
- Stimulate synthesis and secretion of hormones at anterior lobe
Inhibiting hormones (IH)
- Prevent synthesis and secretion of hormones
- Rate of secretion is controlled by negative
feedback
Both hormones are…
- Released from axon endings into capillary bed in median eminence
- Carried by hypothalamo-hypophyseal portal system
- Reaches anterior lobe to regulate secretion of hormones
