20 - Endocrine System

7/27/2019 20 - Endocrine System

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Lecture 19 Endocrine SystemKK Chapter 15, Hildebrand Chapter 20


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Information Systems in VertebratesEndocrine System - chemical signals (hormones) from

the endocrine glands are distributed by the blood-

vascular system to target tissues to regulate the

relatively slow processes of growth, developmentand homeostasis.

Nervous System - receives signals from sense organs,

and transmits them to muscles, to control

movement.


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Thyroid GlandThyroid glands originate as a ventral evagination of

the pharynx, in the vicinity of the gill pouches. The

thyroid hormones are permissive, allowing target

tissues to respond to other stimuli.

Thyroid hormones include thyroxine, and they effect

metabolic rate, growth, development, moulting and

reproduction.

Thyroid hormone precursors

are stored as colloid and are

released in response to

thyroid stimulating hormone

from the pituitary(adenohypophysis).

KK15.1,15.2; H&G 20.2, 20.5


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Other Glands of the PharynxSeveral other glands originate in the pharynx, from

the pharyngeal pouches (and ultimately neural crest),

including the thymus (TM), the ultimobranchial body(B), and theparathyroid (PT). We have alreadymentioned the thymus in the context of hemopoesis.The ultimobranchial body secretes calcitonin, which

lowers blood calcium, and is opposed in this action

by secretions of theparathyroid gland. These areclosed associated with, or embedded in, the thyroid

in mammals.KK 15.5, 15.6, H&G 20.5

Tadpole


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Adrenal Gland

KK 15.8

The adrenal gland develops adjacent to the kidney, and its cortex comes from

mesenchyme. The medulla of the adrenal gland comes from neural crest via

the sympathetic ganglia (which we will cover next lecture). The hormonesreleased by the adrenal gland involve salt and water balance, protein and

carbohydrate metabolism, and stress response.


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Adrenal Gland (2)

KK 15.9, 10

H&G 20.6

There are two components of adrenal glands, adrenocortical tissue

(black below) and chromaffin tissue (white). These are separate in

lower tetrapods. In amniotes, chromaffin tissue is in the medulla ofthe adrenal glands, surrounded by adrenocortical tissue.


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The PancreasThe dorsal pancreas, or the pancreatic islets

where dorsal and ventral pancreas are fused,

also receives neural crest cells. These are

involved in carbohydrate metabolism via the

hormones insulin and glucagon, as well as

protein metabolism.

KK 15.11, H&G 12.12


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Pituitary 1 DevelopmentWe have already

mentioned the origin of the

pituitary (hypophysis) in

the context of the

stomodeum. The adult

organ is compound, arising

from oral ectoderm(adenohypophysis) and

neurectoderm

(neurohypophysis).

KK 15.13, H&G 20.4


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Pituitary 2 NeurohypophysisThe neurohypophysis secretes

vasopressin (ADH) and

regulates water content and

blood pressure. It also secretes

oxytocin, which promotes

release of milk from mammary

glands and also contraction ofthe reproductive organs.

KK 15.15, H&G 20.4


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Pituitary 3 AdenohypophysisThe adenohypophysis secretes

several important hormones,

including growth hormone,

prolactin (lactation), thyroid

stimulating hormone

(thyrotropin: stimulates release

thyroid hormones),gonadotropins (FSH and

LH/ICSH), corticotropin (to

stimulate the adrenal cortex to

release its hormones), and

melatonin-stimulatinghormone.

KK 15.15, H&G 20.4


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Other Endocrine Glands Other endocrine glands include the pineal body

(which we will come to again as part of the

brain), the gonads (testes, ovaries), the

digestive tract, and the kidneys.

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20 - Endocrine System