urine

Uterine Anatomy

Ovary

• Shape and Size: Small, almond-shaped.

Layers of the Ovary:

• Layer 1: Cortex

  • Outer layer.

  • Contains developing follicles.

  • Responsible for the production of oestrogen and progesterone.

• Layer 2: Medulla

  • Inner layer.

  • Supports steroid production in the cortex.

Fallopian Tubes

• Composed of smooth muscle lined with ciliated epithelial and secretory cells.

• Fimbriae: The end of the fallopian tube.

• Ampulla: Typically where fertilization occurs.

Functions of the Ovaries

• Produce fertilizable oocytes capable of undergoing full development.

• Secrete steroid hormones that prepare the reproductive tract for fertilization and support pregnancy.

Gametogenesis

• Definition: The process by which primary follicles undergo meiosis to form gametes.

• Female Gametogenesis: Oogenesis.

• Male Gametogenesis: Spermatogenesis.

Uterus Adaptations During Pregnancy

Uterine Physiology

• During pregnancy and birth, actions of the uterus, fetus, placenta, and membranes must be integrated for optimum growth of the fetus and successful birth.

  • This process requires synchronization of uterine cells and changes in cervical structure and myometrial activity.

  • Signals cascade changes, converting the uterus from a quiescent state to an activated structure at birth.

Uterine Quiescence and Activation

• The uterus must remain quiescent to allow growth and development of the fetus and placenta.

• It has the ability to expel contents during labor.

Structure of the Non-Pregnant Uterus

• Shape and Position: Pear-shaped organ located between the rectum and bladder; is anteverted and anteflexed.

• Functions:

  • Prepares for pregnancy each month.

  • Provides a suitable environment for the growth and development of the fetus.

  • Expels products of conception after pregnancy.

Structure of the Uterus

• The uterus consists of:

  • Cornua: Upper angles where fallopian tubes join.

  • Fundus: Domed upper wall.

  • Corpus: Body of the uterus.

  • Cavity: Interior space of the uterus.

  • Isthmus: Enlarges during pregnancy to form the lower uterine segment.

  • Cervix: Lower portion of the uterus.

• Peritoneum: Broad ligament that connects the uterus to pelvic walls.

Adaptations in Pregnancy

• During pregnancy, the uterus undergoes several adaptations:

  • Becomes thicker and provides a glycogen-rich environment.

  • Uterine blood flow to the endometrium increases from 2% to 80-90% due to low vascular resistance of the placenta.

Adaptation of Myometrium

• The myometrium undergoes structural remodeling to accommodate the growing fetus, transitioning from quiescent to contractile states during labor.

  • Outer Layer: Changes length, contracts, and retracts during labor.

  • Middle Layer: Forms the bulk of the uterus, involved in fetal expulsion and control of postpartum bleeding.

  • Inner Layer: Responsible for distension of the lower segment and dilation of the cervix.

Changes in Uterine Shape During Pregnancy

• At 12 weeks: Uterus has a pear shape.

• At 16 weeks: Fundus takes on a domed shape.

• At 20 weeks: Fundus is at the level of the umbilicus.

• At 30 weeks: Enlarged uterus displaces intestines.

• At 36 weeks: Uterus nearly fills abdominal cavity.

• At 38 weeks: Increased myometrial tone; smoothing and shortening of the lower uterine segment.

Formation of Upper and Lower Segments

• Upper Segment: Formed from the body of the fundus; primarily involved in contraction and relaxation.

• Lower Segment: Formed from the isthmus and cervix; prepared for dilation.

Activity in Pregnancy / Contractions

• Last 6-8 weeks of pregnancy:

  • Development of gap junctions between cells allows rapid spread of electrical impulses, crucial for coordinated contractions.

  • Key Characteristics:

  1. Fundal Dominance: Strongest and longest contractions occur at the fundus.

  2. Polarity: Ensures neuromuscular harmony.

  3. Contraction and Retraction: Pregnant individuals advised to lay on their side (left side preferred) after 30 weeks to prevent suppression of the inferior vena cava.

Braxton Hicks Contractions

• Described by John Braxton in 1872.

• Irregular uterine activity occurring around the middle of pregnancy, increasing in frequency toward term at about 5% per week.

• Purpose:

  • Tone the uterus.

  • Promote blood flow to the placenta.

  • Softening of the cervix in preparation for labor.

Involution of the Uterus

• Uterus reverts to pelvic organ and non-pregnant state over 6 weeks.

• Uterine Fundus: Involutes below the level of the symphysis pubis in 10 days (complete involution achieved by 6 weeks).

Immediate Post-Delivery Changes

• Immediately after delivery, the uterine walls realign, with the fundus positioned below the level of the umbilicus.

• Shape of the uterus becomes globular.

Cervical Changes Post-Delivery

• The cervix loses vascularity and returns to normal consistency within a few days.

• Internal Os: Closes in the second week.

• External Os: Dilation allows for one finger; this can, in some cases, be permanent.

Lochia

• Defined as the loss of excess tissue, which includes blood, leukocytes, shreds of decidua, and organisms.

• Average volume is about 225 ml.

Decrease in Size of Uterus

• Muscle returns to normal thickness due to:

  • Ischemia: Constriction of blood vessels leads to muscle retraction.

  • Endometrial Changes: Superficial layer becomes necrotic and sloughed off as lochia.

  • Size Reduction of Myometrial Cells: Reduces due to decreased levels of oestrogen and progesterone.

  • Phagocytosis: Removal of excess fibrous and elastic tissue post-delivery.

Role of Oxytocin

• Oxytocin stimulates contractions in the uterus.

Ferguson Reflex

• Describe the mechanism of oxytocin release in response to cervical stimulation and subsequent uterine contractions:

  • Baby's pressure on the cervix stretches it.

  • This stretching sends nerve impulses to the brain.

  • Brain stimulates posterior pituitary to release oxytocin, enhancing contractions.