ENDOCRINE SYSTEM Parathyroid Glands 2 paired structures on - PowerPoint PPT Presentation

1 / 41
About This Presentation
Title:

ENDOCRINE SYSTEM Parathyroid Glands 2 paired structures on

Description:

ENDOCRINE SYSTEM Parathyroid Glands 2 paired structures on posterior of thyroid gland. Parathyroid Glands Chief Cells secrete parathyroid hormone (PTH; protein ... – PowerPoint PPT presentation

Number of Views:216
Avg rating:3.0/5.0
Slides: 42
Provided by: lmunetEdu
Learn more at: http://www.lmunet.edu
Category:

less

Transcript and Presenter's Notes

Title: ENDOCRINE SYSTEM Parathyroid Glands 2 paired structures on


1
ENDOCRINE SYSTEM
2
LEARNING OBJECTIVES
Upon completion of this lecture, the student
should be able to
  • Describe the structural organization of the
    thyroid.
  • Outline how thyroid hormone is produced by the
    thyroid follicular cells.
  • Name the hormones that act on osteoclasts and
    kidney tubules and summarize their effects.
  • Describe the cellular organization and components
    of the thyroid follicle.

3
Suggested Readings
Junqueiras Basic Histology Text Atlas 12th
edition
  • Chapter 20 Pages 360 - 369

4
Thyroid Gland
5
Thyroid Gland
  • located anteriorly in cervical region, just
    inferior to thyroid cartilage two lobes
    connected by thin isthmus
  • largest purely endocrine gland in body

6
Thyroid Gland
  • consists of follicles (cuboidal or simple
    squamous epithelium) filled
  • with colloid.

7
Thyroid Gland
  • colloid (composed of the protein thyroglobulin
    containing tyrosine building block of thyroid
    hormones).

8
Thyroid Gland
  • parafollicular cells produce calcitonin

9
Thyroid Gland T4 and T3
  • hormones based on amino acid tyrosine (differ in
    number of iodine ions)
  • thyroxine (tetraiodothyronine T4) and
  • triiodothyronine (T3)
  • T3 is 10x more active, but less common (T4
    accounts for about 90 of all thyroid hormone)
  • Much of the T4 is converted to T3 by liver,
    kidneys, some other tissues

10
Tyrosine and Hormone Derivatives
11
Thyroid Gland T4 and T3
  • affect metabolic rate of every cell in the body,
    except brain, spleen, testes, uterus and thyroid
    gland
  • readily cross membranes (diffuse through plasma
    membrane to bind to mitochondrial receptors and
    receptors in nucleus)

12
T4 and T3 Actions
  • increase synthesis of enzymes involved in
    cellular respiration --gt increase basal metabolic
    rate
  • results in increased heat production.

13
T4 and T3 Control
Release of T3 and T4 is stimulated by TSH
(thyroid-stimulating hormone from adenohypophysis)
Release of TSH stimulated by TRH from hypothalamus
14
T4 and T3 Control
Release of TRH is stimulated by cold, pregnancy,
low thyroxine
15
Thyroid Follicular Cells
  • Thyroglobulin synthesis begins in the rER,
  • Carbohydrate are added in the rER and the Golgi
    complex,
  • Thyroglobulin is releases into the lumen of the
    follicle from vesicles at the apical surface of
    the cell.

16
Thyroid Follicular Cells
2. The uptake of circulating iodide is
accomplished in the thyroid follicular cells by a
membrane transport protein.
17
Thyroid Follicular Cells
This protein, called the Na/I symporter (NIS), is
located in the basolateral membrane of the
follicular cells and simultaneously carries two
molecules, sodium and iodide.
18
Thyroid Follicular Cells
3. Iodide is oxidized by thyroid peroxidase and
is transported into the follicle cavity by an
anion transporter.
19
Thyroid Follicular Cells
4. Iodination of the tyrosine units by thyroid
peroxidase occurs within the colloid.
20
Thyroid Follicular Cells
Under influence of TSH, the follicular cells
engulf portions of thyroglobulin and
colloid. Thyroglobulin is broken down by
lysosomal enzymes into thyroid hormone.
21
Thyroid Follicular Cells
22
Thyroxine control
X
23
Hypothyroidism
  • Most common cause in US chronic autoimmune
    thyroiditis (Hashimoto's thyroiditis)
  • Other causes
  • surgical removal of the thyroid gland
  • radioactive iodine treatment
  • external radiation
  • a deficiency in dietary iodide consumption
    (endemic goiter)

24
Thyroxine control
25
Hypothyroidism
  • a deficiency in dietary iodide consumption
    (endemic goiter)

26
Hyperthyroidism
  • Most common cause Graves' disease an autoimmune
    condition in which the body's immune system
    tricks the thyroid into producing too much
    thyroid hormone.

27
Thyroid Gland Calcitonin
  • polypeptide produced by parafollicular cells.

28
Thyroid Gland Calcitonin
29
Thyroid Gland Calcitonin
30
Thyroid Gland Calcitonin
  • actions decreases blood calcium levels by
  • stimulating osteoblasts (Ca2 uptake and
    incorporation into bone)
  • inhibiting osteoclast activities (osteoclasts
    break down bone matrix releasing calcium)

31
Thyroid Gland Calcitonin
  • control responds directly to blood calcium
    levels
  • very rapid effect

32
Thyroid C cells Ca
calcitonin
Higher Ca
C cells
Negative feedback loop
Lower Ca
Increased kidney excretion increased bone
retention and storage
33
Calcitonin
34
Parathyroid
35
Parathyroid Glands
  • 2 paired structures on posterior of thyroid gland.

36
Parathyroid Glands
  • Chief Cells secrete parathyroid hormone (PTH
    protein)

37
Parathyroid Glands
  • Oxyphil Cells - function unknown

38
Parathyroid Glands
  • actions increases blood Ca2 by
  • stimulating osteoclast activity (which break down
    bone matrix) while inhibiting osteoblasts (which
    form bone matrix)
  • stimulating increased reabsorption of Ca2 by
    kidney
  • indirectly stimulating increased absorption of
    Ca2 by small intestine by causing secretion of
    calcitrol from kidneys

39
Parathyroid Ca
PT Hormone
Lower Ca
PTH cells
Negative feedback loop
Higher Ca
decreased kidney excretion increased bone
resorption (osteolysis)
40
Parathyroid Hormone
41
(No Transcript)
Write a Comment
User Comments (0)
About PowerShow.com