Endocrine System Flashcards
Glands in which ducts carry secretions to surface or organ cavity and have extracellular effects such as food digestion
Exocrine Glands
Glands without ducts which secrete hormones into tissue fluids, capillary networks and the bloodstream
Endocrine Glands
Secretions have intracellular effects, altering cell metabolism
What is the general function of the endocrine system?
Controlling and integrating the function of other organ systems via hormones
What is the difference in nervous vs. endocrine communication?
nervous - electrical and chemical signals
endocrine - chemical signals only
What is the difference in nervous vs. endocrine response speed and effect persistence?
nervous - quick reaction (milliseconds), effect stops quickly
endocrine - slow reaction (seconds to days), effect may continue for weeks
What is the difference between nervous vs. endocrine adaptation to long-term stimuli?
nervous - adapt quickly and response declines
endocrine - response persists
The 3 Main Endocrine System Components
- Endocrine Glands
- Hormones
- Target Cells
Hormone
- a chemical “messenger” molecule secreted into the bloodstream which stimulates a response in another tissue or organ
Target Cells
- cells with receptors for a certain hormone
(ex: thyroid cells are target cells for TSH secreted by the anterior pituitary)
Receptor Site
the site on a cell membrane or in its cytoplasm/nucleus to which a hormone binds
Three Types of Endocrine Glands
- Pure endocrine
- Endocrine/exocrine (mixed)
- “Neuroendocrine” glands
Pure Endocrine Glands
- thyroid
-parathyroid
- adrenal cortex
- thymus
- pineal gland
Endocrine/Exocrine (Mixed) Glands
- pancreas
- ovaries
- testes
“Neuroendocrine” Glands
- Adrenal medulla
- Hypothalamus
- Posterior pituitary
- contain specialized nervous cells which produce hormones
Hypothalamus
- directly below thalamus in diencephalon
- composed of several groups of nuclei ( neurons & neuroglia)
- regulates anterior pituitary hormones
- sends ADH and Oxytocin to posterior pituitary for storage and future release
What is this entire structure?
Pituitary Gland (AKA Hypophysis)
- sits in sella turcica of sphenoid bone
- attaches to hypothalamus via the infundibulum
- secretes nine homeostatic hormones
- two lobes: Adenohypophysis (Anterior, “adeno” = glandular) and Neurohypophysis (Posterior, “neuro” = neural)
What is #4 and what hormones does it secrete?
Anterior Pituitary (AKA Adenohypophysis)
- releases 7 hormones:
- Growth Hormone (GH)
- Prolactin (PRL)
- Thyroid-stimulating Hormone (TSH)
- Adrenocorticotropic Hormone (ACTH)
- Melanocyte-Stimulating Hormone (MSH)
- Follicle-Stimulating Hormone (FSH)
- Luteinizing Hormone (LH)
What is #6 and what hormones does it secrete?
Posterior Pituitary (AKA Neurohypophysis)
- Secretes 2 hormones:
- Anti-diuretic Hormone (ADH) (AKA Vasopressin)
- Oxytocin
What is the fancy latin name for #4?
pars distalis
What’s the fancy latin name for #6?
pars nervosa
A general name for hormones that stimulate other endocrine glands and the 4 of them secreted by the anterior pituitary
Tropic Hormones
- TSH
- ACTH
- FSH
- LH
A general name for hormones that stimulate the gonads and the two secreted by the anterior pituitary
gonadotropins
- FSH
- LH
follicle-stimulating hormone
- stimulates production of egg or sperm cells
Luteinizing Hormone
- stimulates hormone production
males - stimulates interstitial teste cells to secrete testosterone
females - stimulates ovulation and corpus luteum to secrete progesterone and estrogen
Thyroid-Stimulating Hormone
- stimulates growth of thyroid gland and secretion of TH
Adrenocorticotropin Hormone
- regulates stress response by stimulating adrenal cortex
Prolactin
females - stimulates milk synthesis after childbirth
males - increases LH sensitivity, thus increasing testosterone secretion
Growth Hormone
AKA Somatotropin
- promotes tissue growth
Melanocyte Stimulating Hormone
- involved in skin pigmentation
How does the hypothalamus regulate the adenohypophysis?
Via releasing and inhibiting hormones sent through the hypothalamo-hypophyseal portal system
What is a portal system?
- a system in which blood moves from organ to organ without first passing through the heart
What is #9?
Primary capillaries
What is # 2?
Portal Venule
- between hypothalamus and adenohypophysis
What is part #4?
Secondary capillary bed
(in adenohypophysis)
What is #6? And what hormones does it secrete?
Posterior Pituitary (AKA Neurohypophysis)
- secretes two hormones: ADH and Oxytocin
ADH
Anti-Diurectic Hormone (AKA Vasopressin)
- produced in hypothalamus, sent to neurohypophysis, secreted from there
- targets kidneys to increase water retention, reduce urine and increase blood pressure
- functions as neurotransmitter
Oxytocin
- produced in hypothalamus, sent to neurohypophysis, secreted from there
- stimulates lactation and labor contractions
- possible role in sperm transport and emotional bonding
How does the hypothalamus communicate with the posterior pituitary?
Via the hypothalamo-hypophyseal tract, a neural connection between the two glands
- neuron cell bodies in the hypothalamus transport ADH and oxytocin via their axons to a capillary bed in the neurohypophysis
thyroid gland
- the largest endocrine gland
- secrete thyroid hormones which increase metabolic rate, etc.
- located anterior and laterally to trachea, inferior to larynx
- two lobes connected by the isthmus
- bulbous inferiorly, tapered superiorly
the central part connecting the two sides of this gland
Isthmus of the thyroid gland
1 (whole structure, not just cells lining it)
Thyroid Follicle
- microscopic pockets within thyroid filled with colloid and lined with simple cuboidal epithelial cells which release T3 and T4
What are the thyroid hormones and what do they do?
T3 (tri-iodothyronine) and T4 (thyroxine)
- increase metabolic rate and O2 consumption
- increase heat production via calorigenic effect
- increase heart rate and contraction strength
- increase respiratory rate
2 (the liquid within, not the structure)
Colloid, AKA thyroglobulin
- fluid within thyroid follicles containing precursors to thyroid hormones
4
Parafollicular Cells (AKA Calcitonin or C Cells)
- found between cuboidal follicular cells
- produce calcitonin
Calcitonin
- hormone produced by parafollicular cells of thyroid
- Decreases blood Ca2+, promotes Ca2+ deposition and bone formation (via osteoblast activity)
square cells lining circular structures here:
follicular cells
- simple cuboidal epithelium
- produce thyroid hormones
green structure
Pineal Gland (or body)
- located in the posterior roof of the diencephalon
- produces melatonin, which regulates sleep cycles
- may play a role in the onset of puberty
Small, pinto bean-like structures on the surface of the larger structure. (Posterior view)
Parathyroid Glands
- located on posterior surface of thyroid
- usually 4, up to 8
- produce parathormone (PTH) in their chief cells
Parathormone
AKA Parathyroid hormone or parathyrin
- secreted by chief cells of parathyroid
function:
- increase blood Ca2+ levels
- promotes synthesis of calcitriol (active form of vitamin D), thereby…
- increasing digestive absorption of Ca2+
- decreasing urinary excretion of Ca2+
- increasing bone resorption (via osteoclasts)
Calcitriol
- active form of vitamin D synthesized in the kidney when stimulated by PTH
- increases Ca absorption and bone resorption, decreases Ca excretion, thus increasing blood Ca
- opposes action of Calcitonin from parafollicular cells of thyroid
What is the left structure composed of more densely packed cells? And what are its cells called?
parathyroid gland
chief cells - synthesize parathormone
The top, unlabeled lumpy structures
Adrenal Glands
- triangular gland embedded in adipose tissue on superior surface of kidneys
- almost entirely sympathetic innervation
- “two glands in one” - adrenal medulla deep to adrenal cortex
pink interior portion of magnified gland
adrenal medulla
- neuroendocrine tissue
- Chromaffin Cells - modified postganglionic sympathetic cells division of ANS
- create and secrete Epinephrine, Norepinephrine and some Dopamine
- exception to long postganglionic axon rule in sympathetic ANS, preganglionic sympathetic fiber runs into medulla
epinephrine and norepinephrine
- hormones produced and secreted by Chromaffin cells of the adrenal medulla
- have some different effects but generally contribute to fight-or-flight response:
- increase heart rate and BP
- constrict skin and GI blood vessels
- dilate smooth muscle
- increase metabolism
distinct layer of more randomly arranged cells in right half of image sandwiched between two layers of cells arranged in strands
adrenal medulla
(chromaffin cells in spherical clusters)
Chromaffin Cells
- cells of the adrenal medulla which synthesize epinephrine or norepinephrine
Outer layer of gland indicated by pointer
adrenal cortex
- glandular tissue of adrenals
- makes up bulk of adrenal gland
- secretes corticoid hormones
The 3 Types of Corticoid Hormones, Where They Are Synthesized and Examples of Each
- Mineralocorticoids from the Zona glomerulosa, specifically Aldosterone
- Glucocorticoids from the Zona Fasciculata, specifically Cortisol
- Gonadocorticoids from the Zona Reticularis, specifically androgens and testosterone
2
Zona glomerulosa of adrenal cortex
- round arrangements of cells
- make mineralocorticoids, ex: aldosterone
3
Zona Fasciculata
- middle, largest layer of adrenal cortex
- parallel cords of lipid-rich cells
- appear “bubbly” and usually stain lighter than other layers
- creates glucocorticoids, ex: cortisol
4
zona reticularis
- innermost cortical layer next to adrenal medulla
- narrow band of small, branching cells
- produce gonadocorticoids, ex: androgens/testosterone
yellow-white structure extending rightward from the duodenum:
Pancreas
- just inferior to stomach in posterior wall of ab. cavity
- mixed exocrine/endocrine gland
- exocrine cells produce digestive enzymes
- endocrine cells grouped into Islets of Langerhans, which secrete hormones including:
- Glucagon
- Insulin
- Somatostatin
- Pancreatic polypeptide
Glucagon
- secreted by alpha cells of pancreatic islets
- signals the liver to break down glycogen into glucose
Insulin
- secreted by beta cells of pancreatic islets
- signals cells to take up glucose, controls blood sugar levels
Somatostatin
- released by delta cells of pancreatic islets
- decreases insulin & glucagon release
- decreases growth hormone release
Pancreatic Polypeptide
- secreted by F cells (AKA PP cells) of pancreatic islets
- decreases pancreatic exocrine activity
cluster of lighter cells in the middle
Pancreatic Islet (AKA Islet of Langerhans)
- groupings of endocrine cells within the pancreas
- five kinds of cells:
- alpha cells (glucagon)
- beta cells (insulin)
- delta cells (somatotropin)
- F cells (pancreatic polypeptide)
- epsilon cells (ghrelin)
leftmost dark pink area
anterior pituitary
- densely packed cells
middle lighter pink area marked PN
posterior pituitary (pars nervosa)
- unmyelinated axons + neuroglia
4
Thymus
- produces hormones thymopoietin and thymosins which regulate development and maintenance of immune function
paired almond-shaped organs on either side of uterus
Ovaries
- primary female sex organ
- located retroperitoneally in abdomen, lateral to uterus at proximal end of fallopian tubes
- produce female sex hormones estrogen and progesterone and contain ova
Testes
- male sex organ located in scrotum
- secrete androgens (testosterone) and inhibin
- produces sperm cells
Female gametes surrounded by estrogen-producing cells
Follicles
- eggs surrounded by granulosa cells
smaller cells surrounding large central cell
Granulosa Cells
- cells within ovaries that produce estrogen
