Introduction to Endocrine Glands, and Endocrine Glands of the Head and Neck Flashcards
The hallmark of endocrine glands is where they release their products. How is it different compared to exocrine glands?
Endocrine glands release their products into the bloodstream; exocrine glands release their products into ducts.
The cells of endocrine glands have a common morphology except for the thyroid gland. Elaborate on the difference.
The cells of endocrine glands except the thyroid gland tend to aggregate into clusters or cords around blood capillaries that tend to be fenestrated while the cells of the thyroid gland are organized into follicles.
Note:
Fenestration creates gaps in the walls of the endothelium to allow hormones to enter blood capillaries for circulation.
Hormones are biochemical messengers released into the bloodstream. Under the following classes of hormones, state its nature and give examples of hormones under the class:
1. Steroids
2. Amino acid analogues
3. Peptides and glycoproteins
1. Steroids
Nature: Derived from cholesterol
Examples: Gonadal hormones, Corticosteroids
2. Amino acid analogues
Nature: Derived from amino acids (tyrosine or tryptophan)
Examples: Thyroid hormones, Catecholamines, Serotonin & melatonin (serotonin is eventually converted to melatonin)
3. Peptides & glycoproteins
Nature: Made from amino acid chain(s) [+/- carbohydrate]
Examples: Pituitary hormones, Pancreatic hormones
Generally, there are two types of endocrine systems: discrete endocrine system and diffuse endocrine system. Describe each type.
Discrete endocrine system: Endocrine cells are clustered together (to form endocrine glands)
Diffuse endocrine system: Endocrine cells are dispersed (hence no discrete endocrine gland)
The hypothalamus has two-fold endocrine functions. State these functions.
- Produce hormonal factors that regulate the hormonal secretions of the anterior pituitary (termed releasing and inhibiting factors)
- Synthesize hormones that are transported along axons to the posterior pituitary gland and stored there (namely oxytocin and vasopressin)
List the hormones directly released to neurohypophysis (2), and the hormonal regulatory factors released to adenohypophysis (6).
To neurohypophysis:
✔ oxytocin
✔ vasopressin/anti-diuretic hormone
To adenohypophysis:
✔ Prolactin releasing hormone (PRH)
✔ Prolactin inhibiting hormone (PIH)
✔ Dopamine
✔ Somatotropin releasing hormone (SRH)/Growth hormone releasing hormone (GH-RH)
✔ Somatostatin/Growth hormone inhibiting hormone (GH-IH)
✔ Corticotropin releasing hormone (CRH)
✔ Thyrotropin releasing hormone (TRH)
✔ Gonadotropin releasing hormone (GnRH)
The hypophysis cerebri (meaning undergrowth)/pituitary gland is made of two parts reflecting its dual embryologic origin. Name those parts, stating what each developed from. As you know now, these parts are joined anatomically but are functionally separate.
Anterior pituitary/adenohypophysis: developed from ectoderm of roof of the mouth (Rathke’s pouch).
Posterior pituitary/neurohypophysis: developed from neural tube (floor of the diencephalon).
[Diagram: Gross anatomy of the pituitary gland]
[Histological Slide: Pituitary gland]
The adenohypophysis consists of 3 parts. Name those parts.
Pars distalis (anterior lobe)
Pars tuberalis (cranial part)
Pars intermedia
[Diagram]
The neurohypophysis consists of two parts. Name those parts.
- Pars nervosa
- Infundibulum (neural stalk) connecting pars nervosa to hypothalamus. The infundibulum contains the stem and median eminence. The median eminence is a prolongation of the hypothalamus.
- [Diagram]
The neurohypophysis is made up of pars nervosa and neural stalk. Pars nervosa consists of axons of unmyelinated neurons whose cells bodies are located in the hypothalamus. Which hypothalamic nuclei have these cell bodies, and what do each largely secrete?
- Paraventricular nucleus: largely secretes oxytocin
- Supraoptic nucleus: largely secretes vasopressin (ADH)
- [Diagram: Hypothalamic nuclei]
After the paraventricular and supraoptic nuclei synthesize the hormones, they are transported along the axons through the infundibulum through the ____(a)____ tract and eventually accumulate at the terminal endings of the axons as ____(b)____. The rest of the neurohypophysis is made up of highly branched glial cells known as ____(c)____.
(a) hypothalamo-hypophyseal
(b) Herring bodies
(c) pituicytes
oxytocin
(a) location of secretion
(b) target organ/tissue
(c) physiologic effects
(a) paraventricular nucleus of the hypothalamus
(b) myometrium of uterus, mammary glands
(c) causes contraction of the myometrium and ejection of milk by the mammary glands
Antidiuretic Hormonea aka. vasopressin
(a) location of secretion
(b) target organ/tissue
(c) physiologic effects
(d) clinical aspects
(a) supraoptic nucleus of the hypothalamus
(b) renal tubules, blood vessels
(c) water reabsorption, vasoconstriction
(d) diabetes insipidus, syndrome of inappropriate ADH secretion (SIADH)
Outline the classification of the cell types of the adenohypophysis.
✔ The cells of the adenohypophysis can be broadly classified into two categories based on their ability to pick up histological stain: chromophils and chromophobes.
✔ Chromophils are further classified based on the type of stain they have an affinity for: acidophils and basophils. [Acidophils and basophils produce hormones. Chromophobes do not produce hormones.]
✔ Acidophils are further classified based on the type of hormone they produce: somatotrophs [produce somatotropin aka. growth hormone] and lactotrophs [produce mammotropin aka. prolactin].
✔ Basophils are further classified based on the type of hormone they produce: thyrotrophs [produce thyrotropin aka. thyroid stimulating hormone], corticotrophs [produce corticotropin aka. adrenocorticotropic hormone (ACTH)] and gonadotrophs [produce gonadotropins (FSH) and (LH)].
Somatotropin aka. Growth Hormone (GH)
(a) location of secretion
(b) target organ/tissue
(c) physiologic effects
(d) clinical aspects
(a) adenohypophysis, by somatotrophs [type of acidophil]
(b) muscle and bone, liver
(c) promote cell growth and division, carbohydrate metabolism [elevating the levels of glucose in the blood stream]
(d) dwarfism, gigantism [GH excess in early development], acromegaly [GH excess in adulthood]; secondary diabetes
