Canine and Feline Endocrinology and Reproductive Anatomy

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Canine and Feline Endocrinology and Reproductive
Anatomy

• AnS 224
• Spring 2009

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Overview of Endocrinology

• Review of basic endocrinology to provide a better
  understanding of cyclicity
• Emphasis on hormones and the organs/tissues/cells
  involved

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Classification of Biochemical Compounds

• Almost all biochemical compounds can be
  classified into four categories
• Categories are
• Nucleic acids
• Proteins (amino acids and their derivatives)
• Lipids
• Carbohydrates

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Terminology

• Endocrinology
• The study of hormones, the endocrine system, and
  the role in the physiology of the body.
• Endocrine
• secreted internally
• ductless
• applied to organs and structures that release
  their products into the blood or lymph, and to
  substances (hormones) that exert specific effects
  on other organs.

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Endocrine Glands of the Dog
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• Hormones
• a chemical substance produced in the body by an
  organ, cells of an organ, or scattered cells,
  having a specific regulatory effect on the
  activity of an organ or organs.
• For a hormone to exert its function to the body
  it must find its specific receptor.

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Hormone Categories

• Hormones can be classified biochemically,
  depending on their schemes
• Categories are
• Peptides and proteins
• Luteinizing hormone (LH)
• Amino acid derivatives
• Thyroid hormone (T4 and T3)
• Steroids
• Testosterone, estrogen, and progesterone
• Fatty acid derivatives
• Prostaglandins

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Anatomy

• Hypothalamus
• Pituitary
• Hypothalamo-pituitary axis
• Reproductive steroidogenic tissue
• Tissue that synthesizes steroids
• Testis leydig cells
• Ovary ovarian follicle and corpus luteum
• Other players
• Sertoli cells

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Hormones

• GnRH
• LH
• FSH
• Testosterone
• Progesterone
• Estrogen

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Feedback Loops

• Negative feedback loop
• Example
• In the male
• Testosterone has a negative feedback effect on
  GnRH
• Positive feedback loop
• Example
• In female
• Estrogen has a positive feedback effect on GnRH

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Feedback Loops of the Male
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Feedback Loops of the Female
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Overview of Reproductive Anatomy

• Not a class dedicated to Repro anatomy
• Will cover basic topics important to basic
  anatomy and physiology
• Specific areas relevant to anatomy and physiology
  of reproduction in the canine and feline

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Fetal Developmental Reproduction

• Gonads develop at the caudal pole of the kidney
• Female gonad (ovary) remains at this site
• Male gonad migrates to the scrotum, outside the
  body wall, via attachment of the gubernaculum
• Sperm require lower than body temperature to
  develop
• Failure of normal testicular descent
• Cryptorchidism
• Unilateral or bilateral
• Not monorchid
• Mammalian default of the developmental system is
  female

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Anatomy of the Dog and Tom

• Testes (plural), testis (singular)
• Paired organs, produce male gametes (sperm) and
  male androgens (testosterone dihydrotestosterone
  (DHT))
• Tunica albuginea dense tough white connective
  tissue covering testes
• Seminiferous tubules, largest structure in
  testes. Though with a narrow diameter (1/127th
  of an inch), makes up 90 of mass of testes
• sight of sperm production
• Sertoli cells, within seminiferous tubules, aka
  nurse cells or sustenacular cells
• Leydig cells, in testes interstitiaum (outside
  seminiferous tubules), hence aka interstitial
  cells.
• Synthesis of testosterone

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Cross Section of a Seminiferous Tubule
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Spermatogenesis

• Rete testis is a central longitudinal collecting
  duct into which the seminiferous tubules empty.
• Efferent ductules are located at one pole of the
  testes and conduct and concentrate immature sperm
  from the rete testes to the epididymis
• Epididymis anatomically outside testes (palpable
  in the dog), site of sperm maturation.

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Male Anatomy contin.

• Scrotum
• sac-like pouch that houses testes, comprised of
  skin, muscle, and connective tissue
• Testes are somewhat moveable within scrotum
• Torsions
• Cremastor muscles (internal and external -
  striated)
• raise and lower the testes depending on
  temperature
• Tunica dartos muscle (smooth), in scrotal wall
• contracts in cold to keep testes warm
• Spermatic cord nerves, vessels, and ductus
  deferens
• Pampiniform plexus is a vascular plexus for
  counter current heat exchange

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Spermatogenesis

• Occurs in seminiferous tubules by division of
  spermatagonium, and supported by Sertoli cells.
• Spermatagonium are germ cell stem cells. Divide
  to repopulate stems cell population (diploid), or
  to produce sperm (haploid)
• Mitotic vs. meiotic division
• As spermatids mature, they move from the outside
  edge of the seminiferous tubule to the lumen.

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Spermatogenesis
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Spermatogenesis

• Rete testis is a central longitudinal collecting
  duct into which the seminiferous tubules empty.
• Efferent ductules are located at one pole of the
  testes and conduct and concentrate immature sperm
  from the rete testes to the epididymis
• Epididymis anatomically outside testes (palpable
  in the dog), site of sperm maturation.

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Sperm Maturation

• Epididymis (pl epididymides) critical for normal
  maturation and function of sperm
• Found between efferent ductules and ductus
  deferens
• Caput (head) absorbs fluid to concentrate sperm
• Corpus (body) maturation of sperm
• Cauda (tail) storage of fertile sperm
• Innervated for ejaculation
• Epididymitis inflammation of epididymis, usually
  the tail. Scarring causes infertility
• Brucella canis
• Severe inflammation in dog
• Males can cause scrotal necrosis
• Females causes abortions at 40-60 days

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Ejaculation

• Contractions of smooth muscles of epididymis,
  ductus etc propel ejaculate
• Epididymis
• Ductus (ampulla in dog only)
• Abdominal urethra
• Prostate gland (both dogs and toms)
• Penile urethra

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Ejaculate

• Semen sperm seminal fluid
• ejaculate
• Seminal fluid consists of ions (salts), sugars,
  and buffers.
• Activate sperm
• Provides nutrients
• Provides for stable pH
• Provide fluid for lubrication and swimming
• Produced by accessory sex glands

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Male Accessory Sex Glands

• Prostate (dog and tom)
• Clinically important in disease in the dog
• Prostatic abscess
• Bulbourethral gland (tom only), cleanses urethra
  prior to ejaculation
• Seminal vesicles (absent in both)

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Insemination

• Penile anatomy
• Cavernosum tissue
• os penis

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• Bulbis glandis (dog only)
• Responsible for the tie or coital lock
• Penile spines (tom only)
• Responsible for inducing ovulation
• Dependent on testosterone production

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Female Reproductive Anatomy

• Developmental aspects.
• Gonads (ovaries) remain at caudal pole of the
  kidneys
• Anatomy results from degree of fusion of
  Mullerian Ducts, e.g. marsupials

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• Canine and feline
• Bipartite or bicornuate uterus
• Well developed uterine horns, single short
  uterine body, single cervix, single vagina

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Female Gamete Production

• Ovaries
• Produce female gametes (ovum, ova plural)
• Oocytes produced in follicles which develop in
  waves
• Primordial, primary, secondary, antral,
  pre-ovulatory
• Early stages, gonadotrope independent
• Independent of gonadotrophs due to the lack of
  hormone receptors
• Later stages, gonadotrope dependent
• Dependent of gonadotrophs due to hormone
  receptors being present.

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Follicular Development
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Ovulation

• Multiple follicles develop on each ovary
• Canine can have two oocytes per follicle
• Ovulation and follicular fate
• Preovulatory follicle
• Corpora hemorrhagicum
• Corpora Luteum
• Luteolysis
• Corpora Albicans
• Canine ovulates a primary oocyte
• Unusually immature

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Fertilization Of Oocyte

• Ovarian bursa
• Oviduct (one to each ovary)
• Site of oocyte maturation and fertilization
• Three anatomical and physiological distinct
  elements
• Infundibulum (small in bitches and queens)
• Ampulla
• Isthmus
• Connects ovary to uterus

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Uterus

• Tubular structure which supports the fetus
  through the placenta
• A muscular component (smooth) and an epithelial
  component
• Myometrium (muscular)
• Endometrium (epithelial)
• Ectopic pregnancy in the bitch and queen
• VERY RARE could be due to ovarian bursa
• One report in queen

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Insemination/Fertilization

• External anatomy
• Vulva
• Internal
• Vestibule
• Urinary papilla
• Clitoris
• Vagina
• Cervix

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Migration and Implantation

• Sperm deposited in vagina, and via swimming and
  contractions come to anterior aspect of uterine
  horn.
• Fertilization in oviduct
• Developing embryos
• Migrate within uterus
• Migrate between horns
• Evenly spaced
• Implantation via zonary placenta