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Chapter 18: The Endocrine system > 18.3 Endocrine control of growth > Flashcards

18.3 Endocrine control of growth Flashcards

1
Q

Growth in children involves:

A

net protein synthesis, primarily under the influence of GH

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2
Q

True growth entails 3 things:

A
  1. Protein synthesis
  2. elongation of long bones
  3. Increase in size and number of cells in soft tissues
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3
Q

What is the term of the fact that GH has multiple effects within the body

A

pleiotropic

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4
Q

What are the four factors that affect the growth process

A
  1. Nutrition
  2. Genetics
  3. Health
  4. Other hormones
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5
Q

How does nutrition affect growth

A

A balanced diet with adequate proteins and essential amino acids is critical for growth. Malnutrition limits growth potential, while an excessive diet leads to obesity, not increased growth.

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6
Q

How does genetics affect growth

A

Genetic potential sets the maximum growth capacity an individual can achieve, with the other factors determining if this potential is reached.

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7
Q

How does health affect growth

A

Chronic diseases and stress stunt growth. Prolonged stress elevates cortisol levels, Which inhibits growth by promoting protein breakdown, reducing long bone growth, and blocking GH secretion.

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8
Q

How do other hormones affect growth

A

Hormones like thyroid hormone, insulin, and sex hormones contribute to growth, particularly during specific life stages

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9
Q

What hormones drive fetal growth

A

placenta hormones

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10
Q

After birth what hormones take over and regulate growth

A

GH and non-placental hormones

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11
Q

true or false, growth is continuous

A

false

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12
Q

What are the two significant growth spurts

A
  • Postnatal growth
    -Puberty growth spurt
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13
Q

When does postnatal growth spurt occur

A

during the first 2 years of life

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14
Q

Explain puberty growth spurt

A

It is initiated around puberty (11 years old for girls and 13 years old for boys), where long bones lengthen. This period of growth is driven by elevated GH levels and increased secretion of sex hormones. Eventually, these hormones, estrogen in both sexes, halt further bone growth, resulting in adult height.

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15
Q

What cell type grows during the growth spurts?

A

somatic cells

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16
Q

Why is it that even after growth ceases GH continues to be secreted

A

Because it plays a role metabolic regulation

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17
Q

What are the 2 metabolic actions that GH plays (direct effects)

A
  1. Fat mobilisation
  2. Glucose sparing
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18
Q

What is the role of GH in fat mobilisation (fat lipolysis)

A

GH increases fatty acid levels by promoting fat breakdown in adipose tissue

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19
Q

What is the role of GH in glucose sparing

A

It raises blood glucose levels by decreasing glucose uptake in muscles and increasing glucose production in the liver. This spares glucose for glucose-dependent tissues like the brain, which relies solely on glucose but can’t store glycogen

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20
Q

GH exerts most of its growth-promoting effects indirectly through? (GH stimulates for its production)

A

insulin-like growth factors (IGFs) which mediate GH’s influence on tissue to support structural growth

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21
Q

The three ways in which Insulin-like Growth Factors (IGFs) mediate the actions of Growth Hormone?

A
  1. Protein synthesis (decreased amino acid uptake)
  2. Cell division
  3. Bone growth
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22
Q

What is the original name for IGFs

A

somatomedins

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23
Q

IGFs are…

A

peptide mediators structurally similar to insulin

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24
Q

IGFs function by binding to ___________on target cells, triggering signaling cascade through the_____________, which facilitates growth-related effects.

A

receptor-enzymes; tyrosine kinase pathway

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25
Q

What are the two main types of IGFs

A

IGF-I and IGF-II

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26
Q

IGF-I

A

It is stimulated by GH, it mediates most of GH’s growth-promoting actions. The liver is the main source of circulating IGF-I, releasing it in response to GH stimulation. However other tissues produce IGF-I locally for paracrine functions, especially important during postnatal growth.

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27
Q

What are the 3 factors that control IGF-I production and explain them

A
  1. Nutrition- adequate nutrition is essential for IGF-I production. Fasting reduces IGF-I levels despite increased GH secretion
  2. Age: IGF-I production increases dramatically during puberty, contributing to the pubertal growth spurt
  3. Tissue-specific factors- Hormones such as gonadotropins and sex hormones (eg testosterone and estrogen) stimulate IGF-I production in reproductive organs.
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28
Q

IGF-II

A

Unline IGF-I, GH does not influence IGF-II production. It plays a role in fetal development, but in adults its role is unclear

29
Q

GH, primarily through IGF-I, promotes the growth of soft tissue by which two things?

A
  1. Hypertrophy
  2. Hyperplasia
30
Q

What is hypertrophy (stimulated by creatine)?

A

Increasing cell size through enhanced protein synthesis

31
Q

What is hyperplasia (mitosis)

A

Increasing the number of cells by promoting cell division and preventing apoptosis

32
Q

How do i naturally increasing the secretion of GH

A

Jumping up and down and climbing up and down the stairs

33
Q

Why do old people get shorter as they age

A

this is due to the great decrease of GH secretion as people age

34
Q

What is GH’s most dramatic effects

A

promoting the growth of long bones

35
Q

What are the 5 summarised events of long bone growth:

A
  1. Chondrocytes undergo cell division
  2. The older chondrocytes grow larger
  3. As the extracellular matrix calcifies, the entrapped chondrocytes die
  4. The dead chondrocytes are cleared away by osteoblasts
  5. Osteoblasts swarm up from the diaphysis and deposit bone over persisting remnants of disintegrating cartilage.
36
Q

What is bone

A

It is a living tissue consisting of osteoid (organic matrix) produced by osteoblasts (bone formers)

37
Q

Osteoid

A

composed of collagen fibers in a semisolid gel, responsible for the bone tensile strength (resistance to breakage)

38
Q

Calcium phosphate crystals

A

Percipitate within the osteoid, giving bone its compression strength (ability to hold shape under pressure)

39
Q

Bone growth in thickness occurs by:

A

adding new bone on the outer surface of the exisitng bone

40
Q

How does growth in thickness occur

A

Osteoblasts located in the periosteum(outer bone layer) , deposit new bone on the surface. Simultaneously, osteoclasts (bone breakers) dissolve bone on the inner surface next to the marrow cavity, allowing the cavity to enlarge within the bone cirucmference.

41
Q

How does bone growth in length occur

A

It occurs through the activity chondroctyes
(cartilage cells) in the epiphyseal plates (growth plates) between the diaphysis (shaft) and epiphysis (ends of long bones).

42
Q

When do osteoblasts become osteocytes?

A

When they are trapped in the calcified matrix

42
Q

Explain bone growth in length

A

outer edge of epiphyseal plate: chondrocytes undergo cell division, forming new cartilage
Diaphyseal plate: Older chondrocytes enlarge (hypertrophy), pushing the epiphysis farther away from the diaphysis
The extracellualr matrix calcifies thus cutting off nutrients to older chondrocytes, causing them to die. Osteoclasts clear the dead cells, while osteoblasts invade the area to lay new bone, replacing cartilage.

42
Q

What differentiates osteocytes from chondrocytes

A

They remain alive, connected by canals for nutrients and waste exchange

43
Q

What is the function of osteocytes

A

they are involved in calcium regulation in the blood, a process controlled by parathyroid hormone, not GH

44
Q

Gh promotes both lenghtening and thickening of bones through ……..

A

IGF-I

45
Q

GH/IGF-I stimulate long bone growth as long as …………..

A

the epiphyseal plates remain cartilagenous (open)

46
Q

when and how does long bone growth stop

A

during adolescence, sex steroids ossify (close, no futher height increase in height) the epiphyseal plates, permanently halting further lengthening of bones despite the presence of GH and IGF-I

47
Q

What two hormones regulate GH

A

GHIH (somatostatin) and GHRH (dominant regulator)

48
Q

Explain how the two hypophysiotropic hormones regulate GH

A

They do this by binding to the g protein coupled receptors of the somatotropes of the anterior pituitary which are linked to the cAMP pathway:
GHRH: increases cAMP, stimulaggting GH secretion
GHIH: decreases cAMP, inhibiting GH secretion

49
Q

In terms of negative feedback, how is IGF-I the primary inhibitor of GH secretion

A

1.it acts directly on the somatotropes in the anterior pituitary
2. Inhibits GHRH in the hypothalamus
3. Stimulates GHIH in the hypothalamus

50
Q

What five factors influence GH secretion?

A
  1. Diurnal rhythms
  2. Stress, exercise and low blood glucose
  3. Body composition changes
  4. Nutrient levels
  5. Ghrelin
51
Q

True or false: GH levels during early childhood are similar to those of adults, despite the rapid growth observed in childhood

A

true

52
Q

What are the two causes of hyposecretion of GH

A
  1. A pituitary defect leading to low GH production
  2. Hypothalamic dysfunction causing a lack of GHRH
53
Q

What is the condition associatred with hyposecretion of GH in children

A

Dwarfism: occurs when GH secretion is deficient in childhood, leading to short stature due to delayed skeletal growth. other symptoms: Poor muscle development and excess subcutaneous fat ( due to reduced fat mobilization and reduced muscle protein synthesis)

54
Q

what is laron dwarfism

A

It is a condtion where GH receptors are abnormal, causing a lack of response to GH. Despite high levels of GH in the blood, symptoms are similar to GH deficiency

55
Q

What are the three symptoms associated with hyposecretion of GH in adults (after growth is complete)

A
  1. reduced muscle tone and strength
  2. decreased bone density (reduced osteoblast activity)
  3. Increased risk of heart failure due to role of GH in maintaining cardiac mass and performance
56
Q

What is the cause of hpersecretion of GH

A

A tumor in somatotropes in the anterior pituitary

57
Q

What are the two conditions associated with GH hypersecretion

A

Gigantism and Acromegaly

58
Q

What is gigantism

A

This is a condition that occurs during childhood when there is hypersecretion of GH before the epiphyseal plates close. This results in rapid growth in height without body proportion distortion. This condtion can cause individuals to grow over 8 feet tall

59
Q

What is Acromegaly

A

This is when GH hypersecretion occurs after the epiphyseal plates close ( after adolescence) where the bones thicken rather than lenghten. soft tissue proliferates, particularlt connective tissues and skin causing disfuguring conditions.
Bones thicken in the extremities (hands, feet) and face. enlargement of hands, feet, fingers and toes. Apelike appearance.

60
Q

What are the four hormones that are essential for growth

A
  1. Thyroid hormone
  2. Insulin
  3. Sex steroids
  4. Peptide growth factors
61
Q

How does thyroid hormone play a role in growth

A

It plays a permissive in skeletal growth allowing GH to exert its full effects. However it does not directly promote growth. Hypothyroidism in children causes sever stunted growth by hyperthyroidism does not cause excessive growth

62
Q

How does Insulin play a role in growth

A

It supports growth by promoting protein synthesis.
Insulin deficiency can inhibit growth while hyperinsulinism may lead to excessive growth

63
Q

True or false: insulin being structurally similar to IGF-I enables it to interact with the IGF-I receptors which play a role in growth

A

true

64
Q

How do sex steroids (androgens and estrogens) play a role in growth

A

Contribute to the pubertal growth spurt as well as halting further growth by closing the epiphyseal plates
androgens: eg testosterone, powerfully stimulate protein synthesis, increasing muscle mass in males. This contributes to the large musculature in men compared to women.
Estrogen: has a similar role in female growth spurt but does not stimukate muscle mass as strongly as androgens

65
Q

What three factors cause for height differences between males and females

A
  1. Puberty in females occurs about 2 years ealier, giving males more time for prepubertal growth
  2. Boys experience a stronger growth spurt before the epiphyseal plates close
  3. Androgens
66
Q

How do peptide growth factors play a role in growth

A

stimulate growth of specific tissues, eg: epidermal growth factor promotes growth of skin cells

Chapter 18: The Endocrine system (4 decks)

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