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rda > Embryology Part 2 > Flashcards

Embryology Part 2 Flashcards

1
Q

Summarise the development of limbs

A

Upper and lower limb buds form (3-4th week)
They develop into protrusions (7th week)
Upper limbs rotate outwards
Lower limbs rotate medially resulting in a helical pattern of lower extremity dermatomes

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2
Q

What do you call loss of digits?

A

Oligodactyly

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3
Q

Which stage of pregnancy did thalidomide affect?

A

First trimester - affected many organs, particularly upper limb development

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4
Q

Why is thalidomide still used despite its known complications?

A

Useful in:
Cancer
Leprosy

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5
Q

What is the likely mechanism of action of thalidomide?

A

Damages developing blood vessels (upper limb blood vessels more sensitive)
Deprives adjacent cells of nutrients and prevents growth

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6
Q

Why is the timing of administration particularly pertinent with thalidomide?

A

Severe morning sickness occurs around 8th week

Limb development also occurs around this time

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7
Q

How common is kidney development problems?

A

Relatively common, and humans can survive with only one kidney

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8
Q

What name is given to the immature form of a kidney?

A

Pronephros

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9
Q

What do you call a kidney it its intermediate phase of maturation?

A

Mesonephros

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10
Q

What name is given to the most mature form of a kidney?

A

Metanephros

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11
Q

What is the key thing about pronephros and mesonephros?

A

They degenerate and DO NOT give rise to the metanephros; this develops independently

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12
Q

During which week does the pronephros develop?

A

Early 4th week

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13
Q

Summarise the main stages of human kidney development i.e. when the various stages develop and degenerate

A

Early 4th week - pronephros development
6th week - degeneration of pronephros and development of mesonephros
8th week - degeneration of mesonephros and differentiation of metanephric tissue

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14
Q

Describe the movement of the kidney during development and what aids it.

A

Metanephros starts off caudally, and moves rostrally via extension of the ureter.

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15
Q

What happens to renal arteries as the kidney moves upwards?

A

New connections with developing arterial system formed as kidneys move, therefore renal arteries break down and re-form

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16
Q

State three abnormalities of the kidney that can arise during development

A 
Horseshoe kidney (fusion of distal end of two kidneys)
Retainment of one kidney in pelvis 
Retention of an extra artery e.g. underneath ureter-> obstruction of ureter -> enlargement of renal pelvis
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17
Q

What forms within the mesonephros and when are they identifiable?

A

Mesonephric and paramesonephric ducts; identifiable by 5th week

18
Q

Which duct gives rise to male genital ducts, and what is another name for this?

A

Mesonephric duct

also known as Wolffian system

19
Q

Which duct gives rise to female genital ducts, and what is another name for this?

A

Paramesonephric duct

also known as Mullerian system

20
Q

Which layer of the trilaminar disc gives rise to the gonads?

A

Intermediate mesoderm

21
Q

Which cells cover the gonadal precursor?

A

Coelomic epithelial cells

22
Q

Which cells give rise to the gametes and where do these originate from?

A

Primordial germ cells (separate pathway); originate in epiblast

23
Q

Describe the movement of primordial germ cells towards the gonads

A

Originate from epiblast
Migrate to caudal part of yolk sac
Migrate through the hind-gut and dorsal mesentery to mesonephros
Travel from mesonephros to gonads

24
Q

By which week is the urogenital tract neither male nor female?

A

By the 7th week

25
Q

What protein and gene influences differential development of the male reproductive system?

A

SRY (sex-determining region of the Y chromosome)

26
Q

What happens in the absence of SRY and WHEN does this happen?

A

The female tract, gonads and genital pattern develops; 8-9th week post fertilisation

27
Q

What does SRY cause and what is the time frame?

A

SRY causes conversion of the indifferent system to the male tract, gonadal pattern and genital pattern

Over 3 weeks

28
Q

State the key hormone involved in male development, its origin and what stimulates its production and also the regulatory hormone which influences differentiation of indifferent genitalia into male or female structures?

A

Dihydrotestosterone - differentiation (also from Leydig cells)
Testosterone - from Leydig cells supports development of the Wolffian ducts

Testosterone production is stimulated by hCG

29
Q

What is the significance of the timing and stimulation of male development?

A

Male development starts around weeks 7-8 when hCG is also close to its peak

30
Q

What happens to the paramesonephric ducts during male development? State the hormone involved.

A

It regresses due to anti-Mullerian hormone (AMH)

31
Q

Which cells produce AMH?

A

Fetal sertoli cells

32
Q

What else do Leydig cells produce which influences the differentiation of indifferent genitalia into male or female structures?

A

Dihydrotestosterone

33
Q

What are the most common causes of male mal-development?

A

Inability to produce the appropriate hormones

Inability of target tissues to respond to these hormones

34
Q

Give an example and explain a receptor defect leading to mal-development of males

A

Androgen Insensitivity Syndrome - mutant androgen receptor

35
Q

What is another name for androgen insensitivity syndrome?

A

Testicular Feminisation syndrome

36
Q

Explain the presentation of AIS

A

External genitalia look female
Internally, Wolffian ducts are rudimentary or lacking
Testis do not descend

37
Q

Why do people with AIS not develop internal female genitalia e.g. ovaries and uterus?

A

The sertoli cells remain normal, therefore AMH is still produced and stimulates regression of the paramesonephric duct

38
Q

What are the three types of AIS?

A

Mild
Moderate
Complex

39
Q

Name a disorder causing female mal-development

A

Congenital adrenal hyperplasia

40
Q

What is usually the cause of CAH?

A

Mutation in Cytochrome P450 21-hydroxylase enzyme (CYP 21A2)

41
Q

Explain the consequence of the 21-hydroxylase deficiency in CAH and how does this relate to the phenotype?

A 
Limited cortisol synthesis 
No negative feedback on ACTH therefore high ACTH
Over-stimulation of fetal adrenals 
Weak androgen production 
Partial virilisation of genitalia
42
Q

What are the internal systems of somebody with CAH?

A

Still female because there’s no SRY, testosterone or AMH due to lack of Sertoli cells

rda (13 decks)

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