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Chapter 20
*Lecture Outline
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
*See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint
without notes.
Chapter 20 Outline• Endocrine Glands and Hormones• Hypothalamic Control of the Endocrine System• Pituitary Gland• Thyroid Gland• Parathyroid Glands• Adrenal Glands• Pancreas• Pineal Gland and Thymus• Endocrine Functions of the Kidneys, Heart, Gastrointestinal
Tract, and Gonads• Aging and the Endocrine System• Development of the Endocrine System
Introduction
• Endocrine glands are ductless organs.• They secrete their molecular products
(hormones) into the bloodstream.• All endocrine organs have an extensive
distribution of many blood vessels.• The endocrine system and the nervous system
both function to communicate signals throughout the body to bring about homeostasis.– Table 20.1 lists similarities and differences between
the two organ systems.
Comparison of the Endocrineand Nervous Systems
Organs of the Endocrine System
Figure 20.1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ovaries (female)EstrogenInhibinProgesterone
Testes (male)AndrogensInhibin
Pancreatic isletsGlucagonInsulinSomatostatinPancreatic polypeptide
Gastrointestinal (GI) tractCholecystokinin (CCK)Gastric inhibitory peptide (GIP)GastrinSecretinVasoactive intestinal peptide (VIP)
Parathyroid glands(located on posterior surfaceof thyroid)Parathyroid hormone (PTH)
ThymusThymopoietinThymosins
Thyroid glandCalcitonin (CT)Thyroid hormone (TH)
Pineal glandMelatonin
KidneyCalcitriolErythropoietin (EPO)
Adrenal glandsCortex: CorticosteroidsMedulla: Epinephrine (E) Norepinephrine (NE)
HeartAtriopeptin
Pituitary glandAnterior pituitary secretes: Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Growth hormone (GH) Luteinizing hormone (LH) Melanocyte-stimulating hormone (MSH) Prolactin (PRL) Thyroid-stimulating hormone (TSH)Posterior pituitary releases: Antidiuretic hormone (ADH) Oxytocin (OT)
HypothalamusAntidiuretic hormone (ADH)Oxytocin (OT)Regulatory hormones
Overview of Hormones
• Endocrine glands produce informational molecules called hormones.
• Hormones can only affect cells (target cells) or organs (target organs) that have receptors for a specific hormone.
• Cells or organs that do not possess receptors for a specific hormone do not respond to that hormone.
Classes of Hormones
• The study of the structural components of the endocrine system, the hormones they produce, and the effects of these hormones on target organs is termed endocrinology.
• There are three major classes of hormones based on their chemical structure:
1. Peptide hormones—growth hormone2. Steroid hormones—estrogen3. Biogenic amines—thyroid hormone
Control of Hormone Secretion
• Hormone secretion is regulated by a self-adjusting mechanism called a feedback loop.
• There are two types of feedback loops:1. Negative feedback loop
2. Positive feedback loop
Negative Feedback Loop
• In this type of loop, the stimulus starts the process like an elevation in blood glucose (eating a meal).
• The hormone secreted in response to elevated glucose is insulin.
• Insulin brings about a decrease in blood glucose.
Negative Feedback Loop
Figure 20.2
Positive Feedback Loop
• Only a few examples in the human body
• In this type of loop, the stimulus doesn’t produce an opposite and counteracting effect like a negative feedback loop
• The stimulus accelerates the process
Positive Feedback Loop
Figure 20.2
Hypothalamic Control of the Endocrine System
• The hypothalamus The hypothalamus is the interface between the nervous system and the endocrine system and is the master gland master gland of the endocrine system.
• It controls and oversees most endocrine functions.
• It is located in the inferior region of the diencephalon just superior to the pituitary gland.
Mechanisms of Hypothalamic Control
The hypothalamus controls most endocrine activity in three ways:1. Controls release of regulatory hormones from the anterior pituitary gland2. Secretes oxytocin (OT) and antidiuretic hormone (ADH) from the posterior pituitary gland3. Controls the stimulation and secretion activities of the adrenal medulla
Mechanisms of Hypothalamic Control
Figure 20.3
Pituitary Gland
• Also called the hypophysis
• Located just inferior to the hypothalamus
• Housed within the sella turcica of the sphenoid bone
• Connected to the hypothalamus by a thin stalk called the infundibulum
• Divided into anterior and posterior lobes
Pituitary Gland
Figure 20.4
Anterior Pituitary
• Also known as the adenohypophysis
• Divided into three distinct areas:1. Pars distalis
2. Pars intermedia
3. Pars tuberalis
Control of Anterior Pituitary Hormone Secretions
• Hormones secreted from anterior pituitary gland are regulated by regulatory hormones secreted from the hypothalamus.
• These regulatory hormones from the hypothalamus to the anterior pituitary travel through a blood vessel network called the hypothalamo-hypophyseal portal system.
Regulatory Hormones Secreted by the Hypothalamus
Hypothalamo-Hypophyseal Portal System
Figure 20.6
Hormones of the Anterior Pituitary
There are seven major hormones secreted from the anterior pituitary:1. Thyroid stimulating hormone (TSH)2. Prolactin (PRL)3. Adrenocorticotropin hormone (ACTH)4. Growth hormone (GH)—also called somatotropin5. Follicle stimulating hormone (FSH)6. Lutenizing hormone (LH)7. Melanocyte-stimulating hormone (MSH)
Anterior Pituitary Hormones, Target Organs, and Effects
Figure 20.7
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hypothalamus
Median eminence
Anterior pituitary Posterior pituitary
Thyroid
Mammary gland
Adrenal gland Melanocytes
Ovary
Bone
Muscle
Infundibulum
Thyrotropic cells secretethyroid-stimulating hormone(TSH), which acts on thethyroid gland.
Somatotropic cells secretegrowth hormone (GH), which actson all body tissues, especially bone,muscle, and adipose connective tissue.
Pars intermedia cells secretemelanocyte-stimulating hormone(MSH), which acts on melanocytesin the epidermis.
Gonadotropic cells secretefollicle-stimulating hormone (FSH)and luteinizing hormone (LH)which acts on the gonads (testesand ovaries).
Corticotropic cells secreteadrenocorticotropichormone (ACTH), which actson the adrenal cortex.
Mammotropic cells secreteprolactin (PRL), which acts onmammary glands and testes.
Testis
Adrenalcortex
Testis
Adiposeconnective tissue
Posterior Pituitary
• Derived from the embryonic diencephalon
• Comprised of the following regions:– pars nervosa– infundibular stalk
• Neural connection between the hypothalamus and the posterior pituitary is the hypothalamo-hypophyseal tract
Hypothalamo-Hypophyseal Tract
Figure 20.8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Optic chiasm
Anterior pituitary
Posterior pituitary
Infundibulum
Paraventricular nucleus
Supraoptic nucleus
Hypothalamo-hypophyseal tract
Hypothalamus
Telodendria
Pituitary Gland Hormones
Thyroid Gland
• The largest gland entirely devoted to endocrine activities
• Located just inferior to the thyroid cartilage and anterior to the trachea
• Butterfly shape with right and left lobes connected by a midline isthmus
Thyroid Gland
Figure 20.9
Thyroid Follicle
• Functional unit of the thyroid gland
• Comprised of simple cuboidal cells that produce an iodinated glycoprotein called thyroglobulin (TGB) that is stored internally as a colloid
• The follicle cells and the internal storage area for TGB is collectively called the thyroid follicle
Thyroid Follicle
Figure 20.9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Thyroid cartilage
Thyrohyoid muscle
Common carotid artery
Superior thyroid vessels
Trachea
Parafollicular cellCapillary
Follicular cells
Thyroid follicle
Follicle lumen (contains colloid)
(b)
(a)
Cricoid cartilage
Right lobe of thyroid gland
Left lobe of thyroid gland
Isthmus of thyroid gland
LM 400x
Connectivetissuecapsule
Inferiorthyroid artery
Inferiorthyroid veins
a(right): © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel; b(right): © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Parafollicular Cells
• Large endocrine cells located between thyroid follicles called parafollicular cells
• Secrete calcitonin, which helps to regulate serum calcium
Thyroid Gland–Pituitary Gland Negative Feedback Loop
Figure 20.10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
stimulatory
inhibitory
TH
TRH
TSH
1
3
4
5
2
Hypothalamus
TH stimulates target cells to increase metabolicactivities, resulting in an increase in basal bodytemperature.
Increased body temperature is detected by thehypothalamus, and secretion of TRH by thehypothalamus is inhibited. TH also blocks theinteractions of TRH from the hypothalamusand anterior pituitary to prevent the formationof TSH.
Negative feedbackinhibition
A stimulus (e.g., low body temperature)causes the hypothalamus to secretethyrotropin-releasing hormone (TRH),which acts on the anterior pituitary.
Thyrotropic cells in theanterior pituitary releasethyroid-stimulatinghormone (TSH).
TSH stimulates follicular cells of the thyroidgland to release thyroid hormone (TH).
Anteriorpituitary
Target organs in body
Parathyroid Glands
Small glands
(usually four)
embedded on
the posterior
surface of the
thyroid gland
Figure 20.11
Parathyroid Glands
There are two types of cells that are seen in the parathyroid gland:
1. Chief cells (principal cells)—secrete parathyroid hormone (PTH) that helps regulate serum calcium2. Oxyphil cells—function unknown
Cells of the Parathyroid Gland
Figure 20.11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Oxyphil cell
Parathyroid glands
Esophagus
Trachea
Chief cells
Capillary
Oxyphil cells
Chief cells
(a) Posterior view (b) Histologic views
LM 135x
Connective tissue capsuleof parathyroid gland
Thyroid gland(posterior aspect)
Muscles on posteriorside of pharynx
b: © Victor Eroschenko
Parathyroid Hormone
Figure 20.12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bone
Intestine
Kidney
Bloodstream
PTH molecules
1
4
2
3
Ca2+ ions Low blood calcium (Ca2+) levels aredetected by the parathyroid gland.
Parathyroid hormone (PTH)is secreted into bloodstream.
Rising Ca2+
in blood inhibitsPTH release.
Target organs respond toPTH, or its effects, to increaseblood calcium levels:
• Osteoclasts resorb bone connective tissue, releasing Ca2+ into the bloodstream.
• Kidney retains Ca2+ and promotes activation of an inactive form of vitamin D to calcitriol, an active form of vitamin D.
• Small intestine increases absorption of more Ca2+
under the influence of calcitriol.
Thyroid and Parathyroid Hormones
Adrenal Glands• Paired glands anchored on the superior border
of the two kidneys; also called suprarenal glands
Figure 20.13
Adrenal Glands
• Divided functionally into an outer adrenal cortex and an inner adrenal medulla
Figure 20.13
Adrenal Cortex
Three distinct layers of cells (from superficial to deep):1. Zona glomerulosa—produce mineralocorticoids, the main one being aldosterone2. Zona fasciculata—produce glucocorticoids, the main one being corticosterone3. Zona reticularis—produce the sex hormones, estrogen- and testosterone-related hormones
Adrenal Cortex Hormones
Adrenal Medulla
• Forms the inner core of the adrenal gland• Consists of chromaffin cells, which are
modified cells of the sympathetic division of the autonomic nervous system
• These cells secrete norepinephrine and epinephrine
Figure 20.13
Adrenal Cortex and Medulla
Pancreas
• Located between the duodenum and spleen and posterior to the stomach
Pancreas
Figure 20.14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Duodenum
Gallbladder
Celiac trunk
Spleen
Diaphragm
Liver (cut)
Pancreatic islet
Alpha cell
Beta cell
Delta cell
F cell
Spleen
(a)
Alpha cell
Beta cell
Delta cell
F cell
(b)
Pancreatic islet cells
LM 150x
Inferiorvena cava
Abdominalaorta
Body ofpancreas
Pancreaticducts
Bileduct
Duodenalpapilla
Duodenumof smallintestine
Inferiorvena cava
Tail ofpancreas Pancreatic
acinus
Head ofpancreas
Head ofpancreas
Body ofpancreas
Abdominalaorta
Tail ofpancreas
Pancreaticacini
Leftkidney
Bloodcapillary
a: © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel; b: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Pancreas
• Both an exocrine (ducted gland) and endocrine (ductless) gland
• About 98–99% of pancreatic cells are pancreatic acini that produce alkaline pancreatic secretions into ducts
• The remaining 1–2% of cells are small clusters of endocrine cells called pancreatic islets (islets of Langerhans)
• The hormones of the islet cells closely regulate the level of blood glucose
Pancreatic Islets
Figure 20.14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Duodenum
Gallbladder
Celiac trunk
Spleen
Diaphragm
Liver (cut)
Pancreatic islet
Alpha cell
Beta cell
Delta cell
F cell
Spleen
(a)
Alpha cell
Beta cell
Delta cell
F cell
(b)
Pancreatic islet cells
LM 150x
Inferiorvena cava
Abdominalaorta
Body ofpancreas
Pancreaticducts
Bileduct
Duodenalpapilla
Duodenumof smallintestine
Inferiorvena cava
Tail ofpancreas Pancreatic
acinus
Head ofpancreas
Head ofpancreas
Body ofpancreas
Abdominalaorta
Tail ofpancreas
Pancreaticacini
Leftkidney
Bloodcapillary
a: © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel; b: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Pancreatic Islets
Comprised of four different types of endocrine cells, each secreting a different hormone:
1. Alpha cells—secrete glucagon
2. Beta cells—secrete insulin
3. Delta cells—secrete somatostatin
4. F cells—secrete pancreatic polypeptide
Pancreatic Hormones
Pineal Gland
• Secretes melatonin, which is involved in maintaining the 24-hour circadian cycle and sexual maturation
• It is located in the posterior region of the epithalamus
Pineal Gland and Thymus
Figure 20.1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ovaries (female)EstrogenInhibinProgesterone
Testes (male)AndrogensInhibin
Pancreatic isletsGlucagonInsulinSomatostatinPancreatic polypeptide
Gastrointestinal (GI) tractCholecystokinin (CCK)Gastric inhibitory peptide (GIP)GastrinSecretinVasoactive intestinal peptide (VIP)
Parathyroid glands(located on posterior surfaceof thyroid)Parathyroid hormone (PTH)
ThymusThymopoietinThymosins
Thyroid glandCalcitonin (CT)Thyroid hormone (TH)
Pineal glandMelatonin
KidneyCalcitriolErythropoietin (EPO)
Adrenal glandsCortex: CorticosteroidsMedulla: Epinephrine (E) Norepinephrine (NE)
HeartAtriopeptin
Pituitary glandAnterior pituitary secretes: Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Growth hormone (GH) Luteinizing hormone (LH) Melanocyte-stimulating hormone (MSH) Prolactin (PRL) Thyroid-stimulating hormone (TSH)Posterior pituitary releases: Antidiuretic hormone (ADH) Oxytocin (OT)
HypothalamusAntidiuretic hormone (ADH)Oxytocin (OT)Regulatory hormones
Thymus
• Located just superior to the heart and just deep to the sternum
• Larger in infants and children than in adults
• Functions in association with the lymphatic system to regulate and maintain body immunity
Other Organs with Endocrine Functions
Pituitary Gland Development
Figure 20.15
Thyroid Gland Development
Figure 20.16